A character's got an awesome power at their disposal, but there's a catch. Whatever granted the power didn't give the character control over it. They can't stop using their powers, even if they want to. This character suffers from Power Incontinence.
Sometimes, a character will just lose control for an episode or two, or have a few accidents while first learning how to use their powers. Extreme emotional situations may cause a loss of control though, like a pyrokinetic literally Burning with Anger.
Not everyone is so lucky. Many cases are incurable, becoming an integral part of the character. Not to worry, though, chronic power incontinence is treatable with some Applied Phlebotinum. You'll have to hold on to that phlebotinum, though, from now on (try making a snazzy suit out of it). You'll have to depend on it if you want to avoid any accidents or a shorter lifespan.
Note that this is not always a bad thing for the character, since some powers are better when they don't need to be actively controlled. Having the ability to heal any wound, for example, is awesome when you don't have to consciously activate it — otherwise a severe injury might still kill you if you lost consciousness (from loss of blood, say) before switching it on. However, it is always a lack of the Required Secondary Powers that protects a character from their own powers.
Rarely, the inversed set-up of this trope is used; that is to say, rather than the power being hyper-active from lack of control, they can't get it to work in any way.
Can be one of the ways a character is Blessed with Suck. Compare Restraining Bolt or Power Limiter (common methods of averting this) and Does Not Know His Own Strength (a common result of this). If combined with Shapeshifting, this may result in becoming an Involuntary Shapeshifter, depending on what triggers it and how. A character with this may also have a case of I Just Want to Be Normal or Afraid of Their Own Strength. Sometimes terrifyingly applied with Reality Warping Is Not a Toy. Severe cases may develop into a Walking Wasteland.
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As poltergeists differ much from other ghosts, usually having no apparitions and making no noises beyond the mess they cause, there is a theory in occult circles that they actually aren't ghosts, but the observable effects of uncontrolled and unconscious telekinetic ability.
A Doritos advert has two people gaining cold and fire power and finding normal tasks like going the toilet and using deodorant have become problematic.
Miroku has the Wind Tunnel, a black hole-like void in his hand that pulls in everything in front of him unless he has it covered up using his prayer beads. What's worse, eventually the void will be big enough to pull in him (and anything that happens to be around him) unless Naraku is destroyed. It's one of the reasons he keeps asking random women to have his children, so that he'll have a descendant to continue the fight if he fails. The other is that he's a Casanova Wannabe.
Inu-Yasha also has a genetic predisposition to this problem, which his father made a magic sword to fix. After it breaks the first time, the chances of him getting extra power in a way that makes him kind of evil increase dramatically, especially if he doesn't have the sword on him. Luckily it's an awesome BFS which gets continuously upgraded to an Infinity+1 Sword, so he's not missing much, even if a compulsion to kill things didn't bother him.
Yeon Yihwa from Tower of God is an immensely powerful fire user, but she is not only physically clumsy, she has at times so little control over her powerful flames that she has a history of being a Team Killer. She is a little insecure about it.
A-ko does not wear her wrist bands to bed, and in at least one movie was able to throw a pillow to silence an alarm clock without destroying anything. Maybe her powers don't work unless she's fully awake?
Likewise, Rumiko Takahashi's Maris the Chojo wears "strength restraints" since she's a Thanatosian — she has six times the normal strength of a human being. Even with the restraints she still ends up accidentally destroying much of what she touches.
Kyo from Fruits Basket has to keep his prayer beads on whenever he's in human form to prevent him from instantly reverting to his demon form.
Also a major problem for Saki Hanajima. When she was younger, she couldn't block out people's feelings, causing her to become quiet and withdrawn. Because of her refusal to interact with people, she starts getting bullied, until she finally snaps, suddenly discovering her Psychic Powers and using them to put one of the bullies in the hospital.
Kakashi was offered a special eye from his dying friend, but can't turn its power off, so he covers it with his headband in order not to waste energy.
If Naruto reaches four-tails or above then he needs an outside source or the Fourth Hokage to calm him down because he can't on his own, and if given enough incentive or time more tails will come out.
This is actually a very real concern for most jinchuuriki. If too much of the beast's will escapes with the chakra, they'll be overwhelmed and the beast will break out of the seal.
In Darker Than Black, the superpowered "Contractors" must pay for using their powers by performing a pointless action specific to that individual shortly afterwards. Those who don't have to make such a payment are called "Moratoria", suffering from Power Incontinence. Moratoria are stated to be extremely rare, the only one shown in the series having been changed from a normal Contractor as a side effect of a contract-suppressing plant. The same person reverted back into a normal Contractor in the end, something stated to have a near-zero likelihood, but not before going on several uncontrolled rampages wherein she incinerated several people. Sometimes the pointless action makes their powers very much not worth it, like having to drink the blood of children. Or being forced to smoke.
Mao has a Geass that allows him to read the mind of anyone within 500 meters. Over time, he loses the ability to control it and as a result hears the surface thoughts of everyone within range.
Late in the first season, the same fate befalls Lelouch's Compelling Voice Geass; he suffers a brief, debilitating headache, and doesn't realise that he's lost control over his power. He later makes a joke to Euphemia about killing all Japanese people, and realises a moment too late that he's Geassed her into doing it. In the beginning of R2, C.C. gives him a special contact lens to block it when needed. C.C. claims that the contacts will eventually stop working, leaving it active all the time.
And speaking of C.C., she herself suffered this fate back when she had her own geass.
In general, anyone who receives a Geass power will eventually lose control of it.
Vash the Stampede of Trigun could be considered to suffer from this, when Knives releases his Angel Arm.
Minki the Oni from Hell Teacher Nube has incredibly destructive powers... which she loses control of and end up backfiring when she's not wearing her, um, panties.
Played way more seriously when in a fixed day, Nube loses a good part of his control over his Devil Hand. This means his whole arm and then half his body begin mutating. If not for Tamamo, Kyouko and Hiroshi's efforts, he would've been completely consumed by the Hand.
Aki Izayoi, from Yu-Gi-Oh! 5Ds. To make things worse, her Evil Mentor Divine was purposely training her so that her Psychic Powers would be more destructive, as part of his plans to form an army of psychic assassins. After Divine's death, Aki made a Heel-Face Turn that resulted in a slow process that eventually resulted in her being able to control her powers fully... But it wasn't automatic.
The protagonists from the Hoshi no Umi no Amuri OVA, where their abilities are treated like allergies. Amuri's Reflect, causes her to repel physical objects that she touches suddenly, Suzu's Escape causes her to be moving continuously, and Perriere's Infiltrate causes her to pass through most solid objects.
Shaman King: both Hao and Anna have an uncontrollable ability to read minds. This leads to Hao's Start of Darkness and causing further Power Incontinence for Anna in the form of her spontaneously summoning demons.
Negi Springfield's Sneezes of Doom are accidental discharges of magic caused by ordinary sneezes.
His Black Magic ability is also acting up; it's slowly turning him into a demon and causing poisoning-like symptoms in the process, and as the poison and transformation progress, he increasingly goes into Super Mode involuntarily.
The World Tree leaks magical energy all over Mahora's campus for a few days every year. Every 20 years or so, it becomes incredibly powerful, which can lead to some serious problems. Such as a request for a kiss turning Negi into a Determinator or The Big Bad using the energy to power her magic robot army.
In Busou Renkin, the character Victor is constantly displaying a life-draining ability that he can't turn off, even if he wanted to... and so is protagonist Kazuki, who in the later part of the series, begins to turn into a being just like Victor. Justified in that it is a vital life function; Victor compares it to breathing.
Kenichi: The Mightiest Disciple has a variant with Apachai, as he's extremely powerful and is physically incapable of holding back when he fights. As such, he undergoes specialtraining so that he won't accidentally kill Kenichi during training.
Several people in A Certain Magical Index. Touma can't turn his right arm off, so he constantly cancels his own luck and interferes with any magic in the vicinity. Aisa Himegame constantly draws in vampires and kills them en masse. Accelerator suspects that he has such an abnormal appearance because his power deflects sunlight off him, but isn't really sure. Index has no control over her John's Pen mode. Aureolus Izzard needs intense focus to control his alchemist abilities and appears to rely on some type of acupuncture for it, and it still turns on him. As the final major example, the angel that gets sucked down from Heaven really can't help the fact that it has to return and that in doing so it will cause a major catastrophe. It doesn't seem very thrilled about the idea.
Tetsuo starts losing control of his powers following the battle with Kaneda, which manifests as his body starting to mutate around the metal arm he built with them after losing the original to SOL. Eventually, his body starts mutating out of control, leading to the most horrific scene of the movie.
In the movie, Akira himself seems to have this, as he has reached such a power level that when resurrected his powers automatically destroys the city of Neo-Tokyo and then he dissapears into a dimension of his own creation, sucking down everything within a few miles' radius with him.
Clow Reed of Cardcaptor Sakura, Tsubasa Reservoir Chronicle, and ×××HOLiC, reportedly the most powerful magician to ever exist until the coming of his successor, caused the plots of all three series with his power incontinence. He caused the first two by needing to run a Gambit Roulette to get rid of his ability to predict the future (he couldn't turn it off), and he caused the latter two by accidentally turning someone into a zombie simply because while she was dying he wished for her to open her eyes again. The entire multiverse gets fucked up and screwed over several times in trying to fix that booboo.
Coby develops the ability to use Haki (specifically, the Color of Observation) during the war at Marineford. However, his ability to hear voices disappears as people die and it can't seem to be controlled and takes a toll on him during said war.
Luffy had the same problem when he developed Color of the Supreme King Haki. He ended up knocking out everyone in the general vicinity whenever he lost his temper. After the Time Skip, he has full control over it.
After stealing Whitebeard's from his corpse, Blackbeard had a test run of his new Gura Gura Fruit powers and accidentally sent a tsunami at Sabaody Archipelago.
Goku in Saiyuki. When his power limiter breaks or is taken off and he reverts to his true form he will try to kill anything that moves including his friends. He'll probably be reasonably successful as he's immensely powerful in this form. When it breaks the limiter can only be recreated by the gods or Sanzo. Hakkai also has to wear his power limiters although the risk of him losing himself and going berserk when he removes them is only because of the minus wave and when he has been shown to remove them he remains in sane(ish) mind and can put them back on to revert to human form. But he's currently at risk when taking them off, probably.
Translucent is a gentle Slice of Life manga about a girl who's slowly turning invisible. This is presented as a documented medical syndrome, not a special power; at least one adult she knows is permanently invisible. The girl appears more solid when she's feeling self-confident, but will eventually have to learn to find a happy life and accept her condition.
Sket Dance introduces Koma-chan, a ladylike and desperately shy Huge Schoolgirl who is not able to control her enormous strength whenever she's embarrassed.
Coyote Starrk is so powerful that his reiatsu inadvertently killed anything that came near him, leaving him incapable of socialising or forming any emotional ties to others. He was so desperately lonely that he joined Aizen's cause solely because Aizen was the first person he'd ever met who could withstand his reiatsu without dying.
Initially, Ichigo has no idea how to control his enormous reiatsu and when his reiatsu explodes out of him when fighting his very first Menos Grande, he would have died if Uryuu hadn't taken control of his reiatsu for him and calmed it down. Although he gets better at it, he does not have finesse of control and his power output is so great even when in a calm state that he's incapable of sealing his zanpakutou, causing it to exist in a constantly released shikai state by default. His enormous leaking reiatsu also affected several of his classmates, allowing them to become spiritually aware. He possesses a Substitute Shinigami badge that, among other things, acts as a damage limitation device for his reiatsu.
Kenpachi cannot properly control his reiatsu output. As a result, he cannot seal his zanpakutou or control how much reiatsu he's suppressing or releasing so wears a special eyepatch that acts as an artificial Power Limiter. He wears it when he wants to suppress his power and he takes it off when he wants to increase the amount he's using in battle. It's connected to a traumatic childhood experience. His meaningless life gained meaning when he met and almost defeated his first Worthy Opponent. He was so terrified of being left alone that he subconsciously suppressed his power to spare her life and it's been suppressed ever since.
Kotetsu starts showing the first signs of Power Incontinence when his powers starts going haywire in episode 14 — increasing in strength dramatically (jumping manages to cause a sonic boom) but also shutting on and off seemingly at random. It's revealed that he is slowly losing his power, a very rare thing among NEXT, and that his powers going haywire is like a candle flickering brightly before it goes out.
Also the case for his daughter Kaede when she starts to develop her NEXT power. Her power is to copy the ability of the last Next she touches. She can't easily control the first couple of powers she copies, but when Kaede gets Karina's ability she can use it in a variety of ways, probably because she knew what she was dealing with by that point.
Bixlow and Evergreen both have powerful eye magic, which neither of them can fully shut off. (Soul stealing and turning others to stone, respectively.) In order to make sure they don't hurt the people around them, Bixlow covers the upper half of his face with a knight's visor and Evergreen just uses a pair of eyeglasses.
In Wendy Marvell's fight with Chelia Blendy, Wendy uses healing magic on Chelia, powering her up. Everybody wonders what Wendy was thinking, but when Chelia attempts a blast, the attack misfires and misses by a mile. Everybody then realizes that Wendy had been aiming to increase Chelia's powers to the point that she has difficulty controlling them.
In one story from the Miles Edgeworth Case Book manga for the Ace Attorney series, Maya's spiritual powers have developed to the point at which she can unconsciously channel the spirit of her dead older sister Mia merely by thinking about her in her sleep. At the end of the same story, Pearl shows the same ability.
Asa Shigure from SHUFFLE!, as the demonic powers that she inherited from her mom Ama start awakening. She refuses to use them, however, to not break Ama's already damaged heart, and they start to flow so strongly that her life comes to risk. Rin has to force her to use them so Asa won't die due to this trope, taking a knife and slitting his wrists open so Asa will have to heal his nearly fatal injuries.
Haruka Kotoura in Kotoura-san cannot shut off her telepathy, nor can she differentiate between speech and thoughts. She has some limited control over focusing on individual minds to read in all the noise, but if she can't see them she may end up reading any nearby mind. Although she has a few friends now, she's still socially shunned by most because of this.
This is the cause of karma demons in From the New World. They lose subconscious control of their power allowing it to warp their surroundings unabated, leading to very devastating results.
The power that flows from Karasumori in Kekkaishi is revealed to be a form of power incontinence, it simply flows out and infuses everything, partly due to a lack of control and partly due to a lack of ability to consider consequences. Chushinmaru's power is simply out of control, he needed to be sealed because only Hazama could touch him safely (he accidentally siphoned away the lives of an entire village at one point) and so was too dangerous to roam the world. Chushinmaru is incredibly powerful even while sealed, if he was completely free then he would be true menace, even accidentally.
Josuke's stand ability in JoJo's Bizarre Adventure is initially presented as the ability to restore anything and everything (except himself) to a previous state. Then it's quickly revealed that they're actually restored to what Josuke thinks was it's previous state. If he's too distracted or angry to concentrate, the things he restores can be a little...off(at best.)
Oriko, of Puella Magi Oriko Magica, is a powerful Seer with the ability to instantly make predictions of the future. Unfortunately, when she started her career in Symmetry Diamond, she had no control over when it activated and what the subject of the prediction would be. Considering that her magic is Cast from Hit Points... yeah, that was a problem.
Rogue drains the powers of anyone she touches, so she wears gloves and skin-concealing outfits to avoid accidental physical contact with others. Even worse, when she used this power on Ms. Marvel, it didn't wear off for a long time afterwards, absorbing Marvel's powers and memories seemingly permanently. Rogue lives in constant fear that this same thing might happen again to someone else she uses her power on. She was cured of this power incontinence by Professor X in X-Men: Legacy #224. We'll see how long it lasts this time.
Cyclops, without his trademark visor he wears as part of his costume, or a pair of ruby quartz glasses out of costume, would be firing his Eye Beams 24/7. (In fact, he is firing them 24/7, they're just being blocked.) This limitation was recently revealed to be a mental block, and was fixed by Emma Frost. Used to be from having hit his head in the accident that killed his parents. There was a throwaway scene in one of the comics shortly after Wolverine lost his Adamantium (and briefly regressed to a neanderthallic state) where Cyclops hit his head in some kind of rune-covered pit, and a caption stated, "A subtle change is worked in an area of his brain damaged so long ago", so it's possible both explanations are correct. After the events of Avengers vs. X-Men, the visor can't block his eyebeams anymore. The only thing that can are his own eyelids.
Wither has skin secretions that dissolve any organic (that is, biological) matter he touches. Including his father. Good thing he was born into an age of polyester.
Leech's power to turn off other mutants' powers is always on.
Cyclops' brother Havok originally required a special containment suit to control his powers. Interestingly enough, Cyclops and Havok are immune to each other's powers.
When Jean Grey (Marvel Girl, Phoenix) was a child, she couldn't control her telepathic ability and ended up in a catatonic state. Later on she had a similar problem with the Phoenix Force.
One of the residents of the all-mutant neighborhood District X was a woman who could spontaneously burst into flames. Unfortunately, unlike other mutants with similar powers, she was not immune to fire...
Omega Red showed even bad guys suffer from this as he had to drain people's life energy to survive and temporarily had to release the death spores his body built up or they would kill him. Even after he found a cure that allowed him to survive without other people's life he stole it anyway and would probably do the same with his death spores.
Chamber's power is always on, and in fact destroyed half his face and some of his internal organs (heart and lungs) when he first used it. This is what happens if a mutant isn'timmune to his or her own powers. Though it has been established that the fire is actually his true form and his human body is more of a "shell" (or, one might say, a 'chamber') that he doesn't really need, so no real harm done (at least, physically. Half your face being missing tends to put a cramp in one's social life.)
As Gamemaster's omnipathy destroyed his sanity by exposing his mind to the constant horror of 6 BILLION minds all at once all the time, he inserted computer chips into his brain to help regulate his mental activity so he doesn't fry his own brain.
Kitty Pryde became stuck in her intangible phase in the aftermath of an extended period spent hurtling through space inside a giant, ever-hardening bullet that she had phased through the Earth. She was also stuck in intangible mode once after being hit with an energy harpoon during the Mutant Massacre but was restored to normal with the help of Mr. Fantastic and Dr. Doom.
Jubilee can also lose control of her powers if she's angry. (In fact, she once used this to her advantage when she and the rest of Generation X were being held hostage by the mutant criminal Emplate. She insulted him to the point that he was so angry, he used his powers to drain a large portion of her life energy, gaining her powers in the process... Which he could not control, because he was so angry. Suffice to say it turned the situation around.)
After the events of Avengers vs. X-Men, Cyclops, Emma Frost, Magneto, and other mutants who were close to the Phoenix Force are all suffering problems with their powers. Magneto's magnetic powers aren't as strong anymore, Cyclops' eyebeams are too strong even for his visor to contain as mentioned above, and Emma Frost's Psychic Powers aren't working though she can still turn into diamond.
Gambit had to go to Mr.Sinister to have a portion of his brain removed to curb his powers. At the time, he was having difficulty touching things without having them explode, and was worried that people would die because of it. The opperation took him from having the power of an Omega-Level mutant (on par with the like of Jean Grey, Hope Summers and Cable) to an Alpha-Level mutant. The storyline eventually revealed he was right to worry thanks to an encounter with an alternate universe counterpart of his who didn't get the surgery. Said parallel Gambit had changed his name to "New Sun". Because he had awakened to his full powers in a firestorm of energy that incinerated all life on Earth in a few seconds.
Bruce Banner transforms into the Hulk whenever someone makes him too angry, and once he's in that form he has no control over his actions.
Joe Fix-It (a smaller, gray-skinned variant) had a brief story line where he always came out at night and generally did things Bruce did not approve of.
Franklin Richards, the pre-teen son of Reed and Sue Richards of the Fantastic Four. His mutant reality warping powers are practically without limit; he was the one who created the Heroes Reborn universe that saved The Avengers and the Fantastic Four from dying at the hands of Onslaught. However, he rarely has any control of his powers at all. Things... Just seem to happen.
Spider-Man was like this during the Acts of Vengeance storyline. He received the powers of Captain Universe (in order to fight a threat that the Uni-Power predicted would happen after the crisis) but an experiment he was working on with an ESU professor muddled it a little, making him unable to fully control the incredible cosmic powers. This caused horrible mental strain on him, almost pushing him over the edge; he had lived by the saying "With Great Power Comes Great Responsibility" all his life, and now had godlike power. Fortunately, the power of Captain Universe is always temporary; once he had defeated the threat and fulfilled the purpose for which he had been given the power, it went away.
Citizen Steel, one of the newer members, gained the powers of Super Strength and Nigh-Invulnerability through exposure to liquid metal blood. The exposure removed his ability to register temperatures, textures, and (more importantly) how much strength he's exerting. He goes around in a steel costume he's literally welded into to keep him from accidentally crushing anyone.
Another member, Lightning, can't touch anything electrical otherwise she causes it and the the surrounding area to short out, her being a teenage girl who had a popular social life makes it worse for her.
Wundarr absorbed ambient energy constantly, and if it wasn't burned off by occasional acts of Super Strength or dampened by special S.H.I.E.L.D. equipment, he tended to explosively regurgitate it periodically. Later, as Aquarius, his power is modified to neutralize all energy above a certain threshold near him, whether he wants it to or not.
Similarly, Strong Guy of X-Factor has the power to absorb kinetic energy and redistribute it as super strength, but if he doesn't let it out soon enough, it has effects on his physiology (which is the reason for his... unique appearance).
In the Hellboy/B.P.R.D. comics, Liz Sherman has a great deal of difficulty controlling her pyrokinetic powers. Some of this is due to the nature of her abilities, but some of it is also due to psychological trauma related to her first manifestation (at age 11 she destroyed her entire family and 30 other people) and the institutionalized upbringing that followed.
Ghost Rider originally suffered from this, but gained control over his powers eventually.
The character whose murder starts off the plot for Rising Stars is physically invulnerable, but that results in him being unable to have any sense of touch at all. He becomes an obese couch potato because without physical sensation he can't experience any form of physical pleasure except for the taste of food. His murder is carried out when he falls asleep in his chair and he's unable to feel that he's being bound to it by the murderer (who asphyxiates him with a plastic bag).
The Sentry has the problem that he is literally his own worst enemy. Due to a Mind Rape by the old Mastermind, Sentry is completely unbalanced, and displays any number of psychological problems on any given day. He also has some undefined psionic ability to periodically make everyone in the world forget he exists. His biggest problem is that every time he tries to do good with his vast power, he manifests his own arch-nemesis, The Void. The Void then proceeds to do as much evil as the Sentry does good. Which one is working with Norman Osborn?
Zeitgeist, the original leader and Sacrificial Lamb of the revamped X-Force. While this didn't carry on for very long, when his powers (vomiting acid) first manifested, he accidentally killed the girl he was drunkenly making out with on the beach.
Guy Smith, a.k.a. Orphan and Mister Sensitive, led the team thereafter, including when it became X-Statix. His superhuman senses meant that any irritation to his skin caused him great pain. Attempting to block out the pain with mental exercises didn't work; eventually Professor X designed him a special suit.
Phat, one of the members of X-Force/X-Statix under the Orphan, has the power to fill his body with extradimensional gunk, causing it to balloon to grotesque proportions but increasing his strength exponentially. Prior to discovering he was a mutant, he experienced severe fluctuations in weight.
In Watchmen, Dr. Manhattan is tricked into thinking he has this problem.
Mind*** in Empowered can only speak and see using her psychic powers, which makes her unable to lie, because her brother removed her tongue and eyes so she'd be forced to rely on her powers more and reads the minds of everyone nearby; since most of those people are superheroes and most of them are jerkasses, she can't really handle being in groups for long and spends most of her time on their space station alone, which she hates.
The new Superman limited series Secret Origin shows Clark Kent's heat vision going off involuntarily when his emotions are stirred up. The first time fire shoots out is when Lana Lang kisses him, which is... suggestive. At this early point in his life, his glasses serve much the same purpose as Cyclops' shades.
Superman villain Parasite is a little worse off than Rogue stealing life force from anyone near him and being constantly hungry for more.
After being restored to full power on his return from death, Superman's powers started slowly increasing which was welcome at first but eventually led to his powers being out of control and his body physically warped. Eventually cured by having Parasite leech his excess power and the strange element with it that was causing the problem. This also justified an art shift for Parasite from basically looking like a bald man with purple skin to his current more monstrous appearance.
This tends to happen to him periodically because it taps into one of his greatest fears: losing control of his immense power and the harm that could result.
Like Ghost Rider, the first Spider-Woman was at first unable to keep her pheromones in check, causing guys to be attracted to her and woman repulsed at her. She learns to control it, eventually.
Black Bolt of The Inhumans has vast energy powers, comparable or exceeding a Herald of Galactus. Sadly, the region of the brain that controls them is the same that controls his voice. The net effect: he can't open his mouth without unleashing devastation. (Which often gets mistaken for a sonic attack.)
The League of Supermen, a far future team in Superman Annual #8, all suffer from variants of this, due to each having one of Superman's powers (and their artificial nature, as they are all humans genetically modified to simulate Kryptonian powers). Heat has to fire his heat vision every 15 minutes, or he'll burn up from the inside; See-Through has to wear a lead-lined visor when not using his powers; Flyboy has to be tethered to stop him drifting away if he doesn't concentrate; PounderDoes Not Know His Own Strength; and Shield can't feel anything. New recruits Tempest and Speed are given Power Armor that simulates the powers rather than genetic modification; they still have disadvantages (Tempest can't breathe in too sharply; Speed needs to constantly replenish her energy) but at least they can turn them off.
Suntop in ElfQuest has a version of this. Since his power is extreme empathy, he's able to feel the anguish of any elf strong enough to communicate it magically. Even pain from thousands of years into the future. He can't help it, since he's just a child for most of the main plot.
In Ultimate X-Men Gambit joined the evil Fenris corporation because they helped cure his Power Incontinence. He tells Rogue that his energy charging powers had gone out of control and he couldn't even eat — any food he tried to touch would explode.
In Finder, Jaeger's healing factor makes him near impossible to kill, but is so robust he has to get injured regularly to avoid becoming ill.
Negative Man from the Doom Patrol is perpetually radioactive, needing to wear head-to-foot specially treated bandages to contain his condition. This is just one example of the sort of Disability Superpower typical of the team.
Emmy in Demo has a Compelling Voice that she has no control over; it's always on. She tries to get by without talking at all, which generally she can... unless someone's hassling her and refuses to back off, that is.
The Magnet in Terra Obscura. By the time the story takes place, he has almost no control over his magnetic powers. However, they're also not nearly as powerful as they once were, so he mostly attracts coins, staples, and other small objects made from ferrous metals, and even then only when he's within arm's reach of them.
The reborn Emperor in the finale of the Star Wars comic Dark Empire creates a Force Storm to deal with a Rebel fleet parked in front of his enormous battlewagon Star Destroyer. When he's about to be killed by the Skywalker twins, somehow he loses control over the Force abomination and it begins to consume him and his ship in a titanic conglomeration of power.
In the original Creature Commandos stories, Warren Griffith was the team's "Wolfman", but due to an imperfection in the formula that gave him his werewolf powers, he would change to human form and back almost randomly, and typically at the most inopportune times.
When Mina Mongoose first awakened her Super Speed, she had absolutely no idea how to control it, slamming into things at high speeds. She's forced to ask Sonic for help, though she also uses that time to show off her crush for him, too.
When Knuckles accidentally awakens his Chaos Force powers following an attack by the Dark Legion that tossed everyone save Knuckles and a captive Julie-Su into another dimension, he ends up glowing green and accidentally unleashing a lot of power. When the echidnas in Abilon find out about this, they attempt to suck his powers out. All he does is blow up the machine and turn the poor sap at the controls into Doctor Finitevus.
Dungeon Keeper Ami has all individuals, youma or otherwise, trained in Dark Kingdom-style magic exhibit this as a teleportation side-effect. (Lishika is a special example — not only is her affinity lightning but it's strong enough that each teleport will shock any passengers she may be carrying, and once set her on fire!) Also featured are keepers themselves- whose dungeon hearts tend to leak corruption that, in sufficient quantity, takes on the aspect of whatever element/affinity is most closely attuned to the Keeper in question. Examples: Mercury's sleet storm, Zarekos' perpetual night.
Paul in With Strings Attached. At his highest level of strength, he's so powerful that he can barely move without causing chaos. He has practiced literally day and night to get to the point where he can at least walk around, but he has to keep constant watch on himself, keep his arms at his sides, etc. And to revert to his more manageable lower level of strength, he has to explode, creating a large glassy crater and pretty much wiping out everything around him. But even at "low" strength he has to fiercely regulate his behavior.
Shinji And Warhammer 40 K. When Shinji's psychic powers first appear, he's reluctant to depend on them during battle since they interfere with his syncing capabilities. When he does it anyway to win a battle, he has no idea how to turn them off and as such, is booted from NERV. To solve the situation, he embarks on a pilgrimage to Javaal where he learns how to suppress his abilities enough for him to continue piloting and still have enough psychic power to vaporize a human-sized target from a few meters.
In Kyon Big Damn Hero, Haruhi's powers were like this until Nagato started filtering them, though she has to get rid of the junk data every night. Later on, closed space stops being produced, removing the other incontinence Haruhi had.
The Homestuck fanfic four titles interprets Rose's "mind" powers as giving her permanent, uncontrollable telepathy:
There's no way for you to ignore a complex and varied stream of input save doing it consciously. Unfortunately, you can't ignore it consciously; the thoughts of others reach into your mind and fill it with thoughts, tales, ideas.
In Miracle Child, Gamzee can't control the fear-producing chucklevoodoos well because his lifelong habit of sopor slime consumption stopped them from developing normally. This does not endear him to the other trolls.
In Touhou Tonari, this is a serious problem for Yuyuko due to her power to invoke death on others and forced her to isolate herself.
In Always Having Juice, Cream doesn’t know how to control her powers of Super-Imagination. Vector does and is trying to teach her.
In thisSaki doujin, Momo gets too excited while helping Yumi learn how to swim by holding onto her hands and enters "Stealth Mode" by accident (although, in canon, she can't control it and has gone unnoticed for much of her life), terrifying Yumi as she thinks Momo is no longer there.
Dampener removal in Poké Wars results in firing off attacks at random. After control is learned, the attacks are always lethal. In addition, pokémon whose bodies are on fire will start radiating massive amounts of heat uncontrollably.
Demon's Curse: Half the reason Naruto doesn't use his magic (Combination of Vampiric Draining and Dem Bones necromancy) prompting him to ignore them as best as he can. His inexperience at using his magic (and reluctance to use/train said powers) really ends up biting him on the ass when he accidentally transfers a bit of his power to a monster and when a villain made his necromancy go haywire and used him as a conduit to summon a never-ending army. Luckily after the latter incident, Makarov and Mirajane train him to control it.
The Triptych Continuum has her. Due to something going wrong during an attempt to become an alicorn, she is constantly cycling between the three major pony races. Among the results is that she has the raw strength of a Princess for each aspect — and no experience in directing or controlling it. When fear hits, things happen. Some of them can be lethal.
“Oh, oh, right, that! Shit! Uh, hang on a minute, I always forget how to do this –” I concentrated fiercely, and after a few minutes I was pretty sure I had the majority of the Glow dimmed down to a mortal-friendly level. “Better?” I asked, a little nervously. So sue me. I'd like to see you blunder through your first week of Ascension without a bit of performance anxiety.
Films — Animation
The "Sorcerer's Apprentice" scene from Fantasia has Mickey Mouse trying on his master's hat, using his newfound magical powers to animate his broom and have it fetch buckets of water for him. Problem is, Mickey isn't experienced enough with magic to know how to make the broom stop once it's started, and chopping it into pieces with his master's axe only makes things worse, leading to the creation ofmorebrooms withmorebuckets of water, and poor Mickey soon finds himself in way over his head.
Elsa from Frozen can control her powers when she's in a good mood, but if she's afraid or has anxiety, the results can be disastrous, such as her changing the seasons from summer to winter.
Films — Live-Action
In The Adventures of Baron Munchausen by Terry Gilliam, Eric Idle's character Berthold is an extreme super speedster. He wears heavy leg irons to stop himself from dashing all over the place. Similarly, Adolphus, a super sniper with vision that reaches beyond the horizon, wears thick glasses so he can see things nearby; talk about farsighted.
Two Words: Burning Godzilla. Likewise, Larva Battra had no control whatsoever over his eye-beams.
In The Specials, former villain Amok tells of an incident where he lost control of his power to generate anti-matter particles during an... intimate moment, and in his words, "...next thing I know, I'm holding half an ass!"
In X-Men: First Class, Alex Summers can emit powerful energy blasts, but he can't control their direction. This problem is solved by a special harness, which he even refers to as his "energy diaper" in a deleted scene.
Samara Morgan, from the American version of The Ring, is unable to control her ability to project images - whether that's onto surfaces or into people's minds.
The title character of Bruce Almighty had this at first, mainly due to denying he actually had powers, probably meaning that God was just doing it to convince him. Once he'd accepted that he actually had powers, he had no trouble at all in controlling them.
The script however had a few more scenes of the powers apparently acting on their own. One scene would have had Bruce shouting "Damn You!" at an annoying guy at work, causing him to become possessed by a demon, while another scene had him unable to get in the bath, due to involuntarily walking on the water, having to concentrate in order to sink in.
A good number of the Aces and Jokers in Wild Cards have powers that are always on.
Digger Downs's ability to identify Aces or well-disguised Jokers by smell is always on. But so are most normal senses, and they aren't considered incontinent either.
The Amazing Bubbles' ability to absorb kinetic energy and store it as fat is always on. She can't control losing the weight when she fires the bubbles full of energy either.
Bloat's Wall, a surrounding mile-wide field of psychic energy that can only be passed by an intense act of will, and can't be shut off. As Bloat grows, the Wall expands (also against his will) until it reaches parts of the mainland, driving out residents.
Whenever Water Lily as exposed to highly ionized air, she made it "rain". Also whenever she's, um, excited.
In the Halo story The Fall Of Reach it's revealed that if a non-SPARTAN tries to utilize the MJOLNIR armor, they will literally break themselves due to their inability to control their new super-speed and super-strength
Power Incontinence is the entire point of Hidden Talents by David Lubar, where six kids meet at a school for delinquents only to discover they have latent psychic powers that caused their apparent behavior problems. By the end of the first book, they all have better control over their powers except Lucky.
Rae, the main character of the series Fingerprints, can't control her Psychic Powers, and the sudden onslaught of other people's thoughts when her ability first manifests causes her to freak out in public and get committed to a mental institution for a year. She later starts putting wax on her fingers as a sort of makeshift Power Limiter. There's one other character who also can't turn off their psychic ability, but any difficulties they might have aren't directly addressed in the story.
The title character's cursed scar that gives him insight into Voldemort's thoughts.
Not to mention what usually happens to child wizards — they make strange things happen when they're angry or scared. This is evidenced by Harry removing the protective glass keeping a large python inside its cage at the zoo, which made Dudley tumble into said cage. This even carries over into adolescence.
This was the reason why Ariana Dumbledore was locked up at home. After whatever-those-boys did to her she was unable to control her magic and was close to blowing up the house every other day.
Mat Cauthon is extremely lucky. Especially in totally random things-like dice. In fact, he wins so much that people frequently suspect him of cheating and he's forced to leave the scene quickly (sometimes, his luck is kind enough to make him lose to avoid this). Anything and anyone he comes across by random selection will turn out to be important, even when he would much rather avoid trouble.
Several character who can channel (most notably Rand) had trouble keeping a lid on their powers when they were learning the basics. And thanks to a nasty curse, males who learn how to channel end up getting power incontinence all over again since With Great Power Comes Great Insanity.
Aes Sedai can muffle their psychic link with their Warders, but the Warders apparently have no such ability and must rely on the Aes Sedai to do it for them. When Rand and Elayne finally have sex late in the series after several other people are bonded to them, they forget to muffle the bond, resulting in much embarrassment and a near ass-kicking by Birgitte, Elayne's other Warder. It's not so much they forget, they (or at least Elayne) DO muffle it at first but they were um... occupied after that and didnt maintain it.
In Animorphs, after Rachel acquires a crocodile morph, she morphs involuntarily whenever she is feeling strong emotion. There are two reasons why this is a bad thing. The first is that houses are not built to support the weight of an adult African elephant. The second is that when you have a conspiracy of mind-controlling aliens whose only obstacles to taking over the world are the morph-capable "Andalite bandits", it is not a good idea to reveal that you can turn into animals. It turns out that Rachel is "allergic" to the crocodile morph, and once she expels it, she goes back to normal. Except for the fact that she is now standing next to a very confused crocodile...
Janie in Lisa McMann's Wake Trilogy (Wake, Fade, and Gone). Janie has the power to be in other people's dreams. The only problem is, she passes out in the real world and she can't control it. She actually almost gets in a car accident because she got sucked into the dream of a kid on a school bus and passes out and nearly hits the bus.
Gazo Kovacs is a victim of this in the Evil Genius Trilogy: he possesses a powerful and seemingly uncontrollable stench that can knock out just about any human being within thirty paces, and has to wear a hazmat suit to stop it from harming those around him. However, by the third novel, he's managed to get his power under control through various forms of therapy, and is now capable of using it to save lives.
In Stephen King's Firestarter, Charlie McGee's pyrokinetic power first arose when she was a infant, and more than once it nearly kills her and her parents; as she grows older, she does gain some control over it, but this doesn't stop the Government Conspiracy hunting her from fearing that she could become a Person of Mass Destruction unless she's given the appropriate training. It's also worth noting that while she gains the control necessary to avoid starting fires when she doesn't want to, it's very hard for her to stop once she does start one.
Henry, from The Time Traveler's Wife, has no control over his time-jumping ability, which complicates his life as one might imagine, and also leads to some Nightmare Fuel when his offspring inherit the ability - while still in the womb, with usually fatal results.
The Confessors in the Sword of Truth series have to keep conscious control of their power at all times to avoid unleashing it on anyone they touch.
When Colin wakes up after Dahak's "minor improvements" to his body in the first Empire from the Ashes book, he very nearly goes insane from the sensory overload and sensation of an alien presence in his mind. It takes some extended Training from Hell before Colin gets completely used to his new powers.
In The Legends of Ethshar universe warlocks experience this with increasing severity as they develop their powers. Unlike other magical schools, warlocks rely simply on exerting their own will to bend reality; the source of their power does not require bargains, prayers, or rituals to obey them. However, with the passage of time they become increasingly attuned with their powers and so exercise them without conscious thought, often against their own will. This is a bad thing because the more a warlock uses their power, the more they become attuned to the whispers that accompany it. Unless killed naturally, warlocks are eventually drawn to the source of those whispers against their will; the Calling is one of the greatest concerns of their guild.
In Brightly Burning, Lavan Firestorm's gift of Firestarting was provoked into action by bullies at the Merchant's School. He can't control it himself. His Companion and lifebond, Kalira, controls his power. When Kalira is killed in the final battle with Karse, Lavan has neither the means nor the desire to control his gift further. He incinerates the entire region, including the Karsite army, the surrounding forest and grounds, and himself.
This can be an issue for many Gifted until they are taught how to control themselves; in the Last Herald Mage trilogy, Vanyel Ashkevron needs to be removed from the city for everyone's safety after suddenly and traumatically developing his strong abilities, and in the Arrows trilogy Talia loses control of her mental powers even after she's supposedly been taught, because of some misunderstandings regarding her training.
Trisana Chandler was abandoned by her family due to the unnatural weather phenomena that tended to occur around her, which was caused by her magic getting away from her.
Mages in general in the series have minor Harry Potter-style leakage until they learn to control it. The worst affected character is Zhegorz, a man who was assumed to be plain old insane for having visions and hearing voices and was locked up in a Bedlam House until he really did develop paranoid schizophrenia or something like it.
Discussed in The Dresden Files, where just about all mortal wizards have difficulty using technology because their magic "leaks" out into the surrounding environment, generating a "Murphyonic field" (as one character describes it) that disrupts delicate electronics. Simply turning on a phone or computer in the presence of a wizard will cause it to go haywire, and if a wizard is powerful, emotional, or both, it can cause an entire building's worth of electronics to blow out.
Due to a chemical accident, the title character in Confessions of Super-Mom has a warped right hand from which she can spray a mysterious fluid. Not only is she incapable of completely stopping it from dripping, she discovers during a sexual encounter that she... well, sprays at the moment of climax.
In the Lord Darcy stories, prescience is one of the few Talents which has yet to be understood by magical science, and thus, is subject to this trope. Commander Lord Ashley from Too Many Magicians can see a few seconds into the future, but only intermittently when he's under stress.
Thick, in the Tawny Man trilogy, is somewhat mentally handicapped, but incredibly strong in The Skill (a form of mental magic). He often has difficulty not broadcasting strong emotions to everyone within miles of him (and forcing them to feel an echo of what he does).
In the third book of the Knight and Rogue Series Michael has had magic long enough that his powers have adjusted to him and began to trigger on their own, though he's still capable to shutting them down once he notices he's using them.
In Melody and the Pier to Forever, Mathematicians who are untrained may experience power incontinence. In Book 1, Melody struggles to control the Aecxis of Rage and suffers explosions of unintentional or poorly directed aecxal power on multiple occasions.
In the myth of the ancient King Midas of Pessinus, (which is a city of Phrygia): King Midas spoke a prayer in vain, asking for everything he touched to turn to gold. This newly granted enchantment was something that Midas could not control in any way. Everything he touched turned to gold, and he died from starvation as a result of not being able to digest golden things. -According to Aristotle.
Other versions of the myth have him get rid of the power by bathing in the river Pactolus. It caused the river to carry gold ever since, which is how Croesus became rich.
In Cold Kiss by Amy Garvey, Wren's Psychic Powers act up the most when she is feeling overly emotional.
Many of the powers granted by the Swords are like this. Sightblinder, for example, always disguises its wielder, from friend and foe alike. Soulcutter causes soul-crushing despair in everyone within its area of effect, including the wielder. Townsaver and Shieldbreaker both prevent their wielders from putting down either one, or from running away, once battle is joined; Dragonslicer seems to have a similar issue, although the circumstances under which it activates in the first place are much rarer. The Mindsword, when its blade is exposed but it is not wielded by anyone, generates waves of potentially harmful telepathic noise; the Mindsword, when wielded, also affects everyone within its radius, even those whom the wielder might prefer not to mentally enslave.
Another example from the same series is Prince Adrian. In Woundhealer's Story, it turns out that the reason he is blind, and apparently simple-minded, is that he is actually such a naturally powerful wizard that for the first several years of his life, he does not bother using his eyes at all, relying instead on his magical senses. He likewise does not bother trying to talk to anyone, because he has such powerful means of magical communication.
Common in Octavia Butler's Patternmaster universe. "Latent" telepaths, in particular, are entirely unable to control their mind-reading abilities, which makes them miserable people in every sense of the word.
In Croak, Damning comes with unfortunate side effects. Like potentially damning your friends if you don't discharge the energy often enough.
In The Shadow Speaker, Dikeogu has the power of Shock and Awe, however until he learns to control it it pretty much results in lightning randomly hitting him.
Iris from The Ultra Violets has a tendency to "rainbow" when nervous, causing her art beam superpowers to go wild and produce crazy patterns and rainbows at random, and her face to break out in random patterns like lilac flowers, lavender stripes, and violet polka dots.
Imagers in L.E. Modsitt's Imager Portfolio can sometimes use their Imagination-Based Superpower accidentally if they are daydreaming (or just regular dreaming, for that matter). For example, the hero discovers his imaging powers when he starts daydreaming about his master's (he was a journeyman painter at the time) Jerk Ass son blowing himself up by mixing oils wrongly. Next thing he knows: BOOM!!
This also prompts a specific rule that imagers cannot sleep in the same room as any other person, including spouses, because of the risk of killing someone by imaging in your sleep. (This only applies to literal sleep, not sex, as a fair number of imagers are married and have children.)
Orrec's problem in Gifts, the first in the Annals Of The Western Shore. He has no idea when he's actually activated his Deadly Gaze, making him a danger to everyone around him. After destroying an entire hillside and thinking he destroyed his father too, he goes blindfold for everyone's protection. It turns out the real reason he can't tell when he's using his power is because he has no power. His father was just unmaking things from just behind him every time.
Ia of Theirs Not To Reason Why has huge precognitive powers, and anyone who touches her risks being pulled into them, with often traumatic results.
Power Incontinence is the whole premise driving The Greatest American Hero. It's somewhat self-inflicted: the aliens who gave Ralph Hinkley his power-giving super suit also gave him the instruction manual for it, but he promptly lost it (because this is a comedy and hilarity must ensue). And when he got another copy of the manual, he almost immediately lost it again trying out one of the powers described. Hilarity Ensues as he and his FBI agent side-kick make attempts to determine how to activate the suit's various abilities while fighting crime.
There was also an episode where solar flares caused his powers to alternatively super-charge without control and cut out. At one point, he ended up running all the way to Reno by trying to jog... only to end up having to take the bus back.
A major plot point in the first season dealt with Peter Petrelli having to learn to control the powers he absorbs. Power Incontinence seems to be a long-term, almost systemic problem for Peter. When he's under pressure, he seems to get some power, but it's never exactly what he needs (unless he's used it in the past few minutes). If he has time to work at it, though, he can call up a specific power.
Also, Ted, a character with the power to create radioactive energy in his hands cannot control his powers, which caused his wife's cancer and subsequent death.
Maya, who accidentally kills everyone around her whenever she gets upset or separated from her brother.
Dale Smithers had to constantly blast loud Rap music to keep her super-hearing in check.
Sylar is willingly power-incontinent and kills people to get their power. He's regretful afterwards, but can't stop.
Elle, in her second appearance in Volume 3. Sylar apparently cures her with The Power of Love.
Meredith, when she gets injected with adrenalin and can't stop using her fire power.
Mohinder established that the seat of all these powers is the adrenal gland so pretty much any "hero" going through stress or trauma is potentially prone to this.
On The 4400, After taking the promicin shot, Danny gets the ability to spread promicin through the air. He can't stop it without dying himself, and he ends up killing an enormous amount of non-promicin-tolerant people.
Kitazaki from Kamen Rider 555 turns people to ash by touching them. Gaining this horrible power at such a young age (the actor was 15, Kitazaki presumably the same) is probably among the reasons why he has become such a raving madman.
Until he learned to control it somewhat, Chuck suffered from this with the Intersect. Even now in the fourth season, where he pretty much has a handle on it, he will still flash involuntarily on non-combat Intersect entries, i.e. his flashing on Heather Chandler, Sarah's Alpha Bitch in "Chuck vs. the Cubic Z". The flashing is always involuntary. However, he's gained enough control over it able to hide it from people who don't know he's the Intersect, whereas at first he would automatically blurt out whatever he flashed on, then try to cover it up.
Ned in Pushing Daisies suffers from this. It doesn't cause many problems in regard to actually bringing stuff back to life, but it does mean he can never directly touch his dog or his girlfriend or they'll die. Well, he's also forced to be vegetarian, for somewhat squicky reasons. And he can't eat his own pies. And there was the incident with the bearskin rug. But the "not touching his girlfriend" thing is the worst of it.
Tommy Dawkins from Big Wolf on Campus falls under this trope. The poor guy has no control whatsoever over when he transforms into a werewolf whether it be from emotional stress, a full moon, or extreme pain. Though he can transform at will to fight evil. He just has a bit harder time changing back.
Ea, the eponymous heroine of the Dating-Sim story turned TV-Miniseries Toumei Shoujo Ea ("Invisible Girl Ea") was turned invisible by the Random Men in Black before the series starts. This would be a pretty awesome power, except for the fact that she cannot turn it off and several common things both disable it and cause her pain — including static electricity, bright light being reflected off a mirror, and being touched (like, say, by clothes). Trying to find a way to remove her powers so she can live a normal life is a focus of the series.
When Buffy is accidentally infected with a demon's telepathic powers and can't stop reading minds, she nearly goes insane.
Also Willow after the development of her addiction to magic and especially after Tara’s death. At certain point even a minor magic practice triggers personality changes in her and locks a “dark personality↔dark magic” feedback loop.
Also Gwen, who has the power to channel electricity, but unfortunately, lacks the power to not channel electricity.
Also Angel himself, when in Pylea - he gets stuck as a supervampire due to the different laws of physics of that dimension.
In True Blood, it takes a great deal of effort for Sookie Stackhouse to block her telepathic powers.
Sherlock: Although not magical or a superpower, Sherlock's constant deductions about his surroundings cause trouble for him in The Reichenbach Fall. After he is thrown out of a courtroom for contempt because he annoyed the judge by analyzing the jury and refused to stop commenting on the lawyers' questions before they asked them, John tells Sherlock that he told him "not to be clever." Sherlock irritably replies that he can't just turn it on and off.
As of The Empty Hearse, his brother Mycroft shows traces of the same. Sherlock tosses him a hat a client left, asking him to do deductions about his owner. Mycroft refuses, but before he realises he's already started describing the owner.
Kamen Rider Stronger, being the first Kamen Rider with an alternate form, could use his Charge Up to become significantly more powerful. However, he must use the extra energy up within a minute, or else he will explode.
Happens to every villainous protagonist during an episode of the season 2 of Flander's Company, which has the effect to temporarily unlock Docteur Parker's evil Jekyll & Hyde personality.
Bewitched had Esmeralda. When she sneezed, strange objects would temporarily appear, and hilarity would ensure. Also, when she became nervous (and she was nervous a lot), she would become invisible.
One major reason mundane humans distrust telepaths in Babylon 5 is not only that said telepaths can theoretically pry into your mind — they also cannot turn off those abilities. While a deep scan (memories, subconsciousness etc.) requires a deliberate effort, telepaths are constantly, unconsciously surface scanning, i.e. snapping up what people are currently thinking. The only way to avoid is for telepaths to constantly occupy and distract their minds with other stuff. In season five, Byron's renegade telepaths explicitly reject that as an oppressive measure forced on telepaths by mundanes.
Phoebe of Charmed is practically the queen of this trope (not that the other sisters are entirely innocent): She doesn't have any sort of control over her premonitions until ~season 6 (and even then she never learns how to turn it off), the flying power she accidentally stole from the dragon in season 2 was unreliable to say the least. She also had a hard time controlling her empathy power at first, but soon got over that, though she didn't have nearly as much as a rough ride as Prue did when she [temporarily] became an empath. Also happened to Piper "Exit Strategy", where her ability to freeze time is upgraded to Stuff Blowing Up too. Plus, Paige has struggled with this in her orbing ever since she was a high-schooler.
If you think it's tough to break up with someone, just imagine what it's like for Curtis, whose power is to rewind time every time he feels guilty. So he has to constantly find a way to break up with his girlfriend in a way that prevents her from pulling his guilt strings.
Then there's Kelly. Uncontrollable telepathy + poor self-esteem + poor impulse control = hitting people who think bad things about you for no apparent reason.
Not to mention Alisha. Her power to instill uncontrollable lust in anyone she touches sounds pretty weak on its own, but the fact it happens to anyone she touches and that she can't turn it off makes it more of a liability than anything else.
In Mahou Sentai Magiranger, after obtaining their Legend Modes, the siblings experience an overflow of power while in their civilian forms, which is resolved by the end of the episode.
Poor Morgana on Merlin. She's had precognitive dreams her entire life, and even after being trained in magic, she still has absolutely no control over them and needs her magic bracelet to stop them, and even that occasionally fails. It's implied that this is the case with all magic users, as both Morgana and Mordred had no control over their magic when it surfaced.
In Haven, this is the case with practically all of the Troubled; either the power is on all the time, or it tends to activate without their control when they get upset.
Pretty much all of the Cortexiphan kids on Fringe have problems with this when they grow up. One has cell-regenerating powers that given everyone he meets cancer, another has uncontrollable magnetic powers and so can't be near anyone with metal fillings, etc.
In ''The Sentinel Jim often has trouble controlling his senses.
Star Trek has a couple instances where telepaths lose control of their powers and begin projecting their own emotions onto other individuals.
TNG: "Sarek" has the title character begin transmitting his emotions (yes, Vulcans do have them) onto the Enterprise crew due to the Vulcan equivalent of senior dementia, a condition called Bendii Syndrome. This jeopardizes negotiations Sarek has spent almost a century setting up. A mind-meld with Picard enables him to regain control long enough to finalize the treaty.
DS9: "Fascination" has a less serious case where, due to a viral infection, Lwaxana Troi starts to make latent crushes and attractions between the regular cast crop up (Kira and Bashir start making out, Jake Sisko gets a crush on Kira, Kira's boyfriend Vedek Bareil pursues Jadzia who in turn pursues Sisko). Troi's crush on Odo, who wasn't affected at all, started it all.
Ork pskyers, or Weirdboyz, have even less control of their psychic abilities. They generally live apart from the other boyz because the gestalt Waaagh! energy that pervades the Orkish race ends up being vented through the Weirdboy, with negative effects for those around him. In game terms, this means that Weirdboyz must use a psychic power each turn, and the exact ability used is determined randomly. And the power appears randomly, sometimes taking other orks around the weirdboy off.
The Kroot have a Cannibalism Superpower version of Adaptive Ability, allowing them to evolve new traits by consuming the flesh of critters with those traits — eat strong, tough creatures, like Orks, and the Kroot will grow stronger and tougher. The downside is, they can't turn this off, so if they don't eat a balanced diet — and, more importantly, regularly eat the flesh of sapient beings — they'll eventually devolve into mindless animals. The entire animal ecology of their homeworld, Pech, is now based on devolved Kroot.
In GURPS Supers (the rule supplement that fleshed out superpowers), the point cost to buy individual powers can be reduced if the player accepts limitations on them, for example "Always On" or "Uncontrollable", or takes specific disadvantages linked to it. "Body of Fire, Always On" means the character is a walking fire elemental. "Uncontrollable Telekinesis" manifests as poltergeist phenomena. Telepaths who cannot shut their telepathy off suffer massive distraction and headaches if they are in a crowd. Teleporters may find they're not sleepwalking, but sleepteleporting, with embarrassing or life-threatening results.
Many other point-based systems allow that as well, such as Mutants & Masterminds or Big Eyes, Small Mouth. "Uncontrollable" comes with a even worse version of this trope where your power is actively malicious toward you.
The psionics rules for Dungeons & Dragons include a psychic disease known as Cascade Flu, which causes those infected to manifest all their powers, one after another, with random targets. This can be amusing if you have nothing but, say, the powers that create (but not shoot) arrows out of thin air and let you jump really well, but it can be outright deadly if you happen to have more than one attack power.
Cthulhu Tech has this sort of thing with its psychics. Run out of magic points? Don't worry, you can still Cast from Hit Points. You just have a chance of Burning for hours afterwards.
In Ars Magica, this is treated as a fairly ordinary quirk of apprenticeship in the Order of Hermes, especially if the apprentice in question has an affinity for say, fire magic, or, in the case of Bjornaer magi, if they have a particularly ornery or excitable heart-beast form and haven't learned to shift properly yet.
The "broken" creeds of Hunter The Reckoning, Hermits and Waywards, suffer from this, among other things. Waywards have their "second sight" always on, meaning they can /always/ see any monsters around them, non-stop, 24/7. Given that every Wayward is on a personal mission to eliminate the supernatural from the world, this does /not/ do much to help their mental stability. Hermits have a constant connection to the Powers That Be; unfortunately, the human mind wasn't meant to maintain that kind of connection, so the Hermits end up a little unbalanced, as well.
Plenty of Mega-Heroes from Heroes Unlimited have some problem controlling their powers. For example: Hazmat has the powers to control radiation and transform into living plasma. The problem? He can't transform back, meaning he has to permanently stay in a specially designed Hazmat Suit.
This can be a problem with one's party if you get the wrong aura effects in Gamma World. Hi-larity will ensue as your party draws and quarters your character for killing Dave The Robot Demon the hundredth time.
Although it's not necessarily your powers (but it can be), this is how some Afflictions work in Nobilis — they provide a constant stream of miracles whenever the HG thinks they should, but you have no control over which miracles they are or how they are used. One like "My Estate frequently does things in my area without my consent" can lead to much hilarity, although depending on your choice of Estate, this could be anything from randomly inflicting despair on people to the creation of pine cones out of thin air. And you get MP every time an Affliction proves inconvenient to you.
Some Masks of Power are always active, or are simply too much for a normal being, or even a highly powerful being who lacks experience to handle and use properly. Even regular masks need time and practice, but in the case of organic masks (which are actually soft, pulsating living creaturesthat latch onto your face), it can take a lot of effort to shut them down, since they have their own mind. The Toa Inika still made good use of them, since the intense light radiation their heads gave off couldn't be turned down.
Kongu had it worst: he was never able to turn off his Mask of Telepathy (or stop reading minds around him) until he became a Toa Mahri and got another mask.
Then there's the Felnas, Mask of Disruption. As the name implies, it causes whomever the wearer targets to lose control of their powers. This works for the Toa's Elemental Powers, their Kanohi masks, and other species' special abilities. As shown with both Krika and Icarax, disrupting powers like intangibility and teleportation is a very efficient way of killing someone. Both met their end after Gorast did just this with the Felnas she wore.
In Bioshock Infinite, Elizabeth was originally going to grow weaker the more you used her powers, but this idea was dumped due to it being impractical.
In the MMO City of Heroes, an accident suffered during the Rikti War caused the hero Positron's nuclear powers to run constantly, forcing him to spend all his time in his containment suit out of fear of nuking everyone around him. As of Issue 10, though, his powers have gone back to normal, since he was killed when the Rikti invaded again and a teammate resurrected him.
While they aren't specifically superheroes, the Terran Ghosts suffer from being unable to not read thoughts of those around them. At least the superficial stuff.
And Protoss, especially the higher-level ones, sometimes suffer from extreme excess of psychic energy. High Templar units, for example, are in the manual mentioned to go through conditioning so as to not make heads randomly explode in their presence due to extreme psychic power (and relaxing these mental blocks is the basis for their devastating Psionic Storm ability).
In the novel Liberty's Crusade, the title reporter meets Sarah Kerrigan and thinks how great it would be for a reporter to have telepathy, only for Kerrigan to pick up on his thought and simply tell him that it wouldn't be as great as he thinks. In Ghost: Nova, the title character is an extremely-powerful telepath and telekinetic who has yet to learn what she is thanks to her wealthy father carefuly hiding her abilities (any telepath is prompty taken by the Ghost Academy). However, the violent murder of her parents by a terrorist group results in her Mind over Matter abilities to manifest violently in the form of a wave that not only kills anyone still alive in the penthouse but also shatters the glass dome that is supposed to be rated against direct nuclear strikes.
Psycho Mantis from Metal Gear Solid is constantly reading the minds of those around him unless he wears his gas mask. The popular explanation (which was used in The Last Days of Foxhound as well) is that the mask itself doesn't do anything. Rather, it serves as a sort of crutch, like a security blanket or a lucky charm or Magic Feather or something, that allows Mantis to filter out undesirable thoughts.
In the original series of .hack// games, overusing Data Drain caused an array of adverse effects to the player. Depending on how much viral infection the player has taken on from using Data Drain, they can suffer anything from status ailments and debuffs to loss of experience points or even suffer a System Error.
NetHack characters may acquire (either from certain magic items or from eating corpses) the ability to polymorph or teleport... but at random times, uncontrollably. If you're polymorphed into a strong monster during a tough combat or teleported away from danger, good for you! If you're polymorphed into a sewer rat on dungeon level 15, that's a different matter...
And in Ancient Domains of Mystery, may the gods help you if you accidentally teleport out of a shop without paying. Shopkeepers have absolutely no sense of humor.
Freedom Force has Man-Bot, whose Energy-X mutation is much less desirable than those of his teammates. His body constantly builds up volatile Energy-X. He wears a suit of Powered Armor that contains it; without it, he randomly suffers powerful energy discharges that nuke anything in the immediate vicinity... like his brother. It carries over to gameplay as well; even with the armor, any attack that strikes Man-Bot has a small chance of triggering an explosion that damages Man-Bot and anyone close to him. This can be either very good or very bad, depending on whether he's in the middle of the enemy or the team.
The Carson Extreme Hot Rod in Burnout Paradise. Infinite boost is a pretty sweet deal... too bad there's no way to turn it off. If you can master it, though, it's one of the fastest and most fun cars in the game.
inFAMOUS' Cole McGrath can't control his ability to Shock and Awe enough to hold a gun, ride in a car, or even swim.
K' from The King of Fighters has to wear a special glove to control the flame powers given to him by the Kusanagi DNA, otherwise he can cause explosions without trying. A similar character, Nameless, also has to wear a special glove to control his flame powers: at one point in his backstory he killed somebody accidentally by tapping them on the shoulder.
One variant of the "Disease" item in Bomberman causes him to uncontrollably drop bombs. With the charming in-game name of bomb diarrhea.
The Hammer and Golden Hammer in the Super Smash Bros. games could be considered this as while very powerful, once you grab one of them, your character will be forced to swing it like a madman until it either disappears with time or gets knocked out of your hands by an attack, unable to do anything but move and jump until then. Getting knocked off the edge almost ensures your demise due to your inability to double jump or use a special, there are certain things you don't want to hit accidentally (Explosives or an Ike or Marth using a Counter Attack), and if you're unfortunate enough to get a defective hammer that's incapable of causing harm, you can't voluntarily dispose of it.
David, the autistic mathematical genius introduced in the Mass Effect DLC Overlord can understand the Geth and talk in their language. Once plugged in the Geth neural network however, he can't block out any of their constant chattering.
A more pleasant example is Nadia Grell, the Consular's companion in Star Wars: The Old Republic. The poor girl might be one of the most powerful telekenetics in a generation. Unfortunately, Force Sensitives (much less Force Users) are unheard of on her planet. Without training, it led to things exploding whenever Nadia got too happy, too sad, too scared, or too angry. Part of the reason her father was so eager to make an alliance with the Republic (and the Consular, personally) was to find anyone who could help his daughter control her abilities.
Partway through BioShock, Jack ingests a dose of an experimental formula in order to undo Fontaine's Psychic-Assisted SuicideTrigger Phrase. However, its side effect causes him to constantly, involuntarily switch plasmids until he finds and ingests another dose.
The Unbreakable Darkness from Magical Girl Lyrical Nanoha A's Portable: The Gears of Destiny. Merely appearing somewhere causes fluctuations in time and space and creates Dark Piece clones formed from the characters' pasts and even alternate futures. Oh, and the world she's in and everything around it will be reduced to nothing if she ever reaches full power, even though she doesn't want such things to happen. The ending reveals that the Materials and the Tome of the Purple Sky were originally meant to be a Power Limiter system so that she could regulate her unlimited powers, and she's finally able to use them for good once Lord Dearche, the Material of Sovereignty, successfully re-establishes this role of hers.
In Cognition An Erica Reed Thriller, the titular character has the power to briefly look into the past by touching objects imprinted with memories. However, her ability gets extra sensitive if she is emotionally distressed, causing her to involuntary use the power in situations where it is very inconvenient for her.
At the end of every set of stages in Mighty Flip Champs!, Alta's magic wand flips the chambers on its own, so she has a very short time to move to a safe spot to avoid getting crushed by the incoming dimensional wall.
The same thing happens in the final stage of Mighty Switch Force!, where Patricia's helmet siren activates every few seconds without her input.
Shiki sees lines of death on everything, allowing him to destroy nearly anything with even a butterknife. Shortly after acquiring this effect, he started having nightmares of the world falling apart at its seams and would have gone insane if he had not been given indestructible glasses that block this effect. Using this power anyway puts a strain on his brain and usually gives him headaches when he takes off the glasses. In the manga, he also kills things with a tree branch and his finger nails.
On a lighter note, Seo Akira can see the future... sometimes. With the amazing control to know that Shiki will decide on impulse to invite her to chat after lunch. On a plus note, seeing the future doesn't lock it in place for her like most forms of clairvoyance, which also means that the above chat after lunch doesn't necessarily ever happen.
Likewise, in Fate/stay night, Rider wears a eye visor constantly, not just to hide that she's Medusa, but also the fact that her petrification ability from her eye cannot be restrained. Or if she's in her normal mode, she wears a pair of glasses. The exact same style of glasses as Shiki's actually — they're called Magangoroshi (Mystic Eye Killer) glasses. Seeing as Aozaki Touko is one of the few connections between the Tsukihime and Fate timelines, as she's the one who makes Shirou his artificial body, it's very likely she also made Rider's glasses, as she made Shiki's as well.
Two important examples in Da Capo, though only one really minds. Sakura's magic is highly dependent on her emotions and acts out in ways she wouldn't normally. As a child, her magic would accidentally break people's arms. In the main story, a girl gets a branch dropped on her head in Sakura's route and there are implications that she is accidentally responsible for Nemu's sickness in that route. Kotori is the other example, who often feels fatigued and ill due to constantly reading the minds of others, especially their more negative thoughts or ones in which she is the school idol, not a person.
In (P)lanets, the purpose of the academy is to teach psychic students how to control their powers.
Marin has a harder time controlling her psych than other students because she wasn't born with it. As a telepath, she had to learn to turn it off so she wouldn't hear everyone's thoughts all of the time.
Ryuu has trouble controlling his teleportation and runs out of energy quickly due to a heart condition.
Kaius doesn't use his powers Pure Energy because it is too dangerous and before he knew how to control them he accidentally killed his mother.
Zimmy has Reality Warper powers. They tend to spontaneously manifest by making her nightmarish hallucinations become real. Either that or the power only has one setting; it's really not clear at all how it works, or if the hallucinations are caused by the power or merely coexist with it. Although the point still stands that she can't control it. The closest she can come to controlling it is by sticking close to a Power Nullifier, which is far from a perfect solution. (Especially since her Power Nullifier of choice is subject to human needs like sleep.)
Elliot and Ellen from El Goonish Shive experience what is perhaps one of the most literal forms of this possible; to the extent that Elliot is instructed to use his transformation powers in the privacy of a bathroom at every opportunity so as to prevent "accidents." In fact, anyone who gains their magical powers "improperly" will have some form of Power Incontinence until their magic power stabilizes.
Ben of Breakpoint City can't control his lightning blasts without the gloves given to him by the superhero organization.
Jigsaw Forte from Last Res0rt learns about her Vampiric powers the hard way, right down to having to either learn to control her temper or risk letting her more... visual aspects manifest themselves. She can't turn her mind-reading off, either, which makes her have panic attacks around crowds.
Witches in Serenity Rose have good control over their powers for the most part, but can conjure up creatures in their sleep. Sera creates a monstrous version of a girl she once knew, which results in a hiker losing his arm, and later results in the violent dismemberment of many of the soldiers sent to stop it. Another witch, who never consciously used his powers at all, supposedly created 100 giant fire-breathing metal horses to crush Napoleon's army. He was of course burned alive, being a witch in the 19th century and all.
Faen in Drow Tales has the ability to feel the emotions of those around her, and at times can control those emotions. Which would be pretty awesome if a) she could turn it off, b) she didn't live in a Crapsack World, or c) she weren't essentially Purity Personified. Eventually, the constant Mind Rape drives her slightly nuts, she accidentally kills off a significant number of people, and she ends up fleeing to the surface world, at which point the main character follows her.
Kili of The Dragon Doctors has such powerful spiritual senses that they went totally out of control when she was a child; she's been branded with magical marks on her face and body that suppress her spiritual vision to keep her from going insane. What remains of her power is still immense, since it turns out these tattoos completely negate the powers of ordinary shamans.
In the world that Dan and Mab's Furry Adventures is set in there exists the authors own design of what incubi and succubi are, essentially a race of shape shifting empaths who feed off emotions more than they do souls. Unfortunately for those individuals who mature to a point where this function becomes active without someone in the know to instruct them, these individuals may suffer from crushing migrains due to the influx of constant emotional downpour around them. Thankfully this can be for the most part filtered to allow only the desired emotional energies to flow through 'but' recently it's been revealed that despite this the cubi in question will always be 'very' susceptible to the emotions around them such that whatever emotion they may be experiencing at any given time will be kicked into overdrive so that even the slightest bit of anger becomes blinding rage for those who lack restraint.
After losing his arm, Dies Horribly from Goblins is bestowed with a shapeshifting magical one, but the new limb also reacts to emotions, making it hard to control, as it will transform into spikes and blades when he is scared. He never learns to fully control it, especially once the arm develops an ultra-violent mind of its own and ultimately has to sever it causing it to transform into an ultra-powerful, mindlessly aggressive, multiplying evil being that sustains itself on the blood of the living.
The Chosen Four shows Ness loses control of his PSI as a result of emotional trauma, becoming an Unstoppable Rage. Department Store Spook learned that the hard way.
One subplot in Wapsi Square involves Shelly's inability to control her sphinx side. She's partially shapeshifting whenever she feels strong emotions, and her instincts are interfering with everyday life.
In the middle of the "Gackt" arc in Manly Guys Doing Manly Things, Mr. Fish (a Gyarados) learns Hyper Beam. The problem is that once he starts Hyper Beaming, he can't stop. He Hyper Beams Gackt in the face and then runs out of steam.
Jared: COMMANDER! WE DON'T KNOW HOW TO TURN OFF THE LASERS!
The "Jareth's cold" arc of Roommates is made of this trope. Every time poor guy sneezed something random magic happened, he even managed to sneeze the creator into the comic.
Katia Managan, protagonist of Prequel, suffers this as she learns to control her magical abilities.
Karin-dou 4koma: Seren is an immortal magician of immense power with a "Spell Booster" predisposition that automatically, drastically boosts any spells she casts, rendering low-level magic impossible without her Power Limiter on.
Kit Darling in Poppy O'Possum has the power to see matter at the atomic level, as well as potential interactions between substances. Unfortunately, she has no control over this power; she's been functionally blind since she was a young child, and can only manage with the help of special anti-magic glasses.
Hawthorne dorm at Superhero School Whateley Academy in the Whateley Universe has a bunch of people with this problem — it's what the dorm is for. Frostbite manipulates any water around her and freezes it, but isn't immune to the cold she creates. Diz has a PK field that has a force of over eight tons — and she can't stop it. Everything she touches get hit with eight tons of force. She has to take liquid food (and presumably air) through a special deviser-built nano-tube straw because her forcefield keeps everything out, so she hasn't had solid food since her powers came on.
The biggest is Sara who has fire generating powers with the power to ignite and burn whole towns; the catch...she can only control it while awake normally, so when she sleeps or is knocked out everything burns.
There are others who have power problems, although mostly minor or often background mentions, the Undergrounder's who have powers that either do not fit, make them difficult to live with, or out right monsters. A main character who suffers from this is Boris who's power of super digging comes from his huge and very sharp claws..which he can't retract or hide in anyway.
Silence/ Simon from Phaeton can't talk due to his inability to disable his sonic vaccum field.
SCP-507 of the SCP Foundation will randomly shift to a random Alternate Universe version of Earth, and then shift back to his original universe after a random amount of time. He has absolutely no control over this, so the only thing he can do is carry emergency supplies with him at all times so they'll be with him when he shifts.
A number of characters in Worm suffer from this to one degree or another. A woman with the ability to make people suggestible through her songs told her ex to "go fuck himself" without realizing she was affecting him. He did. Fatally. Another example is Panacea, who accidentally brainwashed her foster sister into being in love with her.
Gloom Glimmer suffers from this in Brennus. Her Adaptive Ability tries to give her what it thinks she needs, constantly - such as clairvoyance for every odd thought, or a powerful sexual glamour when she wants to impress her new teammates. She takes special pills to rein it in.
Generally averted with Popeye, who can maintain control well under the influence of spinach. However, in at least two shorts Popeye force-feeds Bluto spinach, who then proceeds to lose all control and involuntarily and senselessly beats Popeye up (in both shorts, Bluto has reasons for not doing so).
One episode introduced an alternate version of Red Star, essentially the Soviet Captain America, and a crapload more powerful. Problems arose when it was revealed that his body periodically discharges a highly corrosive and dangerous plasma like substance. In a true Tear Jerker moment, Red Star was revealed to have lived in exile his whole life in a compound built to contain him after he accidentally destroyed half of his hometown.
Beast Boy tends to change shapes randomly when he sneezes, such as in the episode when he caught a cold.
The title character of Danny Phantom has this problem, especially at first. Even later, hormones and extreme emotion cause his powers to bleed over to his human form, although limited to glowing eyes (when angry) or bouts of invisibility/phasing (particularly when around an attractive girl). He also had a hard time learning to duplicate.
His two strongest powers repeatedly gave him problems. His Ghostly Wail would use up all his ghostly energy and cause him to revert back to his human form after using. When he first manifested his ice powers, they caused him to feel like he was freezing, to the point where he eventually was. All of these problems were solved by the end of the series and he was in complete control of his powers.
A second season episode of W.I.T.C.H., "U is for Undivided", has Cornelia's younger sister Lillian began to manifest her Heart of Earth powers, making her as powerful as Elyon. Without even knowing it, she gave her cat Napoleon the ability to speak, and transformed her family's apartment building into a medieval castle. The girls and Matt had to arrange a complex plan to get Lillian to unknowingly pass off her powers to Matt, Mr. Huggles, and Napoleon, keeping the girl Locked Out of the Loop about her abilities until she reached the age where she'd be able to handle her powers responsibly.
In The Spectacular Spider-Man, the Villain Of The Week Max Dillon gets zapped by lab equipment and thrown into a tank of electric eels; this being a version of the Marvel Universe, he starts constantly emitting electricity, and has to wear a protective suit at all times so other people won't be hurt. Even so, his power leaks out - he can't watch TV, lighting arcs out of his hands when he's upset - and he can't even eat without zapping something. By the time he gets into a supervillain teamup, of course, he's managed more control.
Occurs in Transformers Animated when Sari gets in touch with her heritage and ends up with more power than her system and low level of control can safely handle, causing her to go on a rampage. It was even lampshaded.
Ian Peek from the episode "Sneak Peek" gets his hands on an experimental belt that allows him to pass through walls. Repeated use renders the belt unnecessary, but unfortunately for Ian, without the belt he's not up to the task of regulating when and what he passes through. Guess what happens.
Derek Powers a.k.a. Blight, the Big Bad for season 1. Powers became a Walking Wasteland in the show's beginning. He managed to pass for human by applying a fake skin; however, it degraded after time. Anyways, as Batman continuously foils his schemes, Powers undergoes a season-long Villainous Breakdown which causes the fake skin to degrade even faster; eventually, his temper means that the skin wastes away too quickly for him to continue running his corporation. He then undergoes a rather literal Superpower Meltdown, though its implied he might've survived.
In the "Only a Dream" episode, John Dee a.k.a. Doctor Destiny traps several members of the Justice League in their worst nightmares. Three of them have nightmares related to Power Incontinence. The Flash gets stuck in Super Speed mode so that Time Stands Still for him. John Stewart's concerns that his new powers as a Green Lantern have permanently altered and isolated him from humanity are taken to an extreme (poor guy literally cracks up as Green light bursts out of his body!). The worst is Superman. His powers go out of control and he accidentally kills the people closest to him.
The Flash: I've always been afraid this would happen. I'm gonna live out my whole life in the time it takes you to tie your shoelaces! Somebody! Say something! (curls up in a fetal position)
Green Lantern: Come back! Why are you all running? What are you afraid of? (as his friends and neighbors all run away when they see him)
Superman: I started out with no power at all. Then I kept getting more. What if it never stops?
On a side note, Dee didn't do this to Hawkgirl. He just took advantage of her claustrophobia and trapped her in a nightmare where she was Buried Alive.
In a later episode, Flash pushes his powers to the limit to take down a particularly tough foe (who's just wiped the floor with the rest of the League)... and then discovers he can't slow down. If not for The Power of Friendship, he'd have been lost in the Speed Force forever, and says outright that he can never do that again.
Likewise, J'onn tries to extend his telepathy to all of Metropolis in order to do a quick scan for Lex Luthor in "Tabula Rasa." He finds him... and then gets flooded with the private thoughts of all of Metropolis, and finds he can't shut off the flow.
Occurs in Avatar: The Last Airbender with Aang's Sneezes of Doom, with a variety of "oops" levels including accidental blown roofing. Aang also has the problem of reflexively entering the Avatar State whenever he's under emotional duress. When he does, duck and cover. Should you happen to be the focus of his wrath, put your head between your knees and kiss your butt goodbye.
In the Static Shock episode "Sunspots", the titular hero begins to lose control of his electromagnetic abilities after being exposed to sunspots. Sometimes his abilities cease to work altogether, while other times, he becomes overpowered to the point that he almost harms those around him.
Spyke slowly gained this problem. In the third season, he had increasing trouble retracting his spikes, to the point where he simply couldn't do so. Then he was Put on a Bus until the fourth season, where his spikes had grown into full-blown bone armor he couldn't remove.
The episode "Power Surge" does this to Jean, who loses her hold on her telekinesis and telepathy.
Rogue went even wilder when all the personalities and powers she had absorbed resurged and caused her to flip out.
In Ben 10, Ben's NRG form is made of Pure Energy, with control over fire and radiation. Unfortunately he has to stay encased in a special suit of armor, or the people around him can develop radiation poisoning.
Ben in general himself suffers from this, as at times the Omnitrix would give Ben something other than the form he had in mind.
In the episode "The Cutie Mark Chronicles", Twilight Sparkle flashes back to her entrance exam for Princess Celestia's School for Gifted Unicorns. In the course of taking the test, she taps into her latent magic for the first time and ends up accidentally leaking magic all over the place, turning her parents into potted plants, among other things.
A milder example occurs in "The Ticket Master" when, accosted by a crowd of ponies who want her ticket to the Grand Galloping Gala, Twilight Sparkle unexpectedly teleports herself and Spike away to the library. Twilight is merely surprised, but Spike ends up shocked... rather literally.
As her Sanity Slippage gets worse in "Lesson Zero", she starts to Teleport Spam without even apparently realizing it during the picnic with her friends.
During the events of "The Cutie Pox", Apple Bloom steals some of Zecora's ingredients to brew a potion that could finally grant what she desires the most: a Cutie Mark. The problem is, the potion effect doesn't stop at one and keeps giving her an infinite number of Cutie Marks (every new Cutie Mark gives her a new special ability, to boot) and Apple Bloom neither can turn them off or stop using her new abilities. Eventually, her body ends up acting on its own, without stopping to rest or sleep while Apple Bloom desperately begs it to stop.
The existence of "Princess Celestia's School for Gifted Unicorns" and "Magic Kindergarten", which are entirely separate schools for unicorns focused on teaching them to control their powers, imply that power incontinence is a fact of life for all unicorns, at least in early childhood. Confirmed when, after the Cake twins are born, Rarity warns the parents that baby unicorns are prone to strange, unpredictable bursts of magical energy.
In Twilight's Kingdom Part 2, once she's been supercharged with the other Princesses' magic, Twilight is so overpowered that the mere act of opening a door instead causes it to explode and trying to fly sends her off at a speed which breaks the sound barrier.
In The Venture Bros., Cody Impossible has the power to turn himself into a human torch but lacks the Required Secondary Powers to either turn it off or be immune to the pain of being set on fire. Any amount of time he spends awake and in a normal oxygenated atmosphere is an unending torment of unimaginable pain.
Duman in Winx Club eventually becomes sick and has trouble controlling his powers. This indirectly leads to his death.
Combo Ninos: In one episode, Diadoro and Gomez released a Divino who had the power to turn into anyone who touches him, regardless of the Divino wanting it to happen or not.
Early in Season 1 of Avatar: The Last Airbender , Katara suffered from Power Incontinence while she was learning how to Waterbend properly. When she gets flustered or angry, her subconscious Bending is strong enough to split building sized icebergs, but once she gets some proper training near the end of the season she quickly becomes a Waterbending master.
In Steven Universe, the title character has trouble activating, and controlling, his powers. He is a child as well as being part human, though, and controlling his powers is suggested to be something he can learn.
Truth in Television with baby skunks. Adult skunks can control when they release their scent (and usually give plenty of warning before they resort to it, because it does take a lot of energy to produce). Baby skunks, however, don't have the necessary control over their scent glands yet, in much the same way other infants suffer from regularincontinence.
Similarly, it has been observed that venomous snakes will inject different doses of venom in different situations, using more to defend itself from a predator than it would use in capturing prey, for example. Many biologists believe that young snakes are less able to control the doses they deliver than adults; making it that much harder to treat the victims of bites from younger snakes.