Plotting to destroy the planet is a good source of conflict for your standard Evil Overlord, but, when it comes right down to it, destroying the world isn't really a very effective Evil Plan — especially if it's the world the Evil Overlord is living on: it's where he keeps his stuff. Basically, plotting to destroy the planet is a good way to demonstrate that you're evil, but there are hardly any situations in which this sort of destruction is going to have any sort of value for the villain.
Once this is understood, you find yourself in the curious situation where the sort of fellow who goes around destroying worlds isn't actively evil. More often, he's more a sort of buffoon. A guy who just doesn't have the sense of responsibility or the ability to wrap his mind around the consequences of his actions to realize that blowing up a planet is a particularly bad idea.
Compare with the Omnicidal Maniac, the "serious" version of this trope who can wrap his head around the concept and wants to do it anyway. If this goes to the next step and the destruction is only really caused by the character's indirect actions, then the character is a Doom Magnet (though the normal version of this also applies as well).
Not to be confused with Woobie, Destroyer of Worlds, who wants to destroy everything because of past mistreatment. Can be considered a subtrope of Nice Job Breaking It, Hero.
The Dirty Pair have accidentally blown up at least ten planets, though it's only ever an indirect result of their actions.
In the Sailor Moon anime, Sailor Saturn is theoretically capable of destroying the world just by bringing down the tip of her weapon. Thing is: she's a protagonist. So in the anime, she only ever starts doing this as a threat against certain Big Bads but someone always has to stop her. In the manga, she actually does destroy the world, just once, at the end of the Death Busters arc. Since this is Sailor Moon and the main character has "reviving people and/or planets" explicitly as a power, it recovers. The manga also notes that Saturn slumbered during the Silver Millenium until the Talismans carried by Neptune, Uranus, and Pluto awoke her after the Moon Kingdom's destruction, causing her to also destroy the remnants of the Kingdom and allow a new world to be reborn (along with herself and the other Outer Senshi).
Jirarudan from Pokémon 2000 nearly wipes out the world's ecosystem by tampering with some very important, very pretty elemental birds. Destruction isn't part of his plan; only the birds are, and he never comes across as evil, only greedy and blissfully unaware of what he kickstarted.
More of a major territory destroying incident: in Turn 18 of Code Geass R2, Suzaku accidentally nukes the Tokyo settlement with FLEIJA when his Geass command overrides his wish to die in battle. The explosion kills off 30 million people both directly and indirectly, destroys a large portion of the city and completely shatters the Japanese´s trust in Britannia.
And played for maximum effect in the big WHAM Episode of the first season: Lelouch experiences Power Incontinence at the worst possible moment during the Special Administrative Zone when conversing with Euphemia, causing her to interpret a geass command to "kill the Japanese", which incites a massacre of said Japanese that is only stopped when Lelouch tearfully shoots his sister.
In the Dragon Ball series attempting to blow up planets is a common occurrence.
Super Buu almost destroys the entire physical universe by powering up.
Kid Buu destroys several planets during his rampage.
Buu deserves special mention as depending on who he's absorbed his whole mind changes. As Super Buu (initially) he shows some awareness of his actions and desires to fight and destroy, after absorbing Piccolo he becomes a lot more eloquent about it and shows that he relishes the thrill of annihilating anyone strong and wants to be the strongest thing by killing everything else. Kid Buu is essentially a feral animal that just lashes out in rage and destroys earth simply because it's there, seemingly lacking a conscience or a rational mind (despite being able to learn quickly). Majin Buu (the fat one) acts as a weird intermediary between the two: possessing childlike innocence and having absorbed two cosmic gods he thinks that destroying worlds is a game because his creator told him it was but when the consequences of his actions are explained to him he decides that blowing up planets and killing people is a bad move.
Beerus is an even straighter example. [[Dragon Ball Z:Battle Of Gods]] ends with him eating wasabi sauce and by jumping around he destroys a couple of planets.
The title character of Haruhi Suzumiya unconsciously sends off giants to attack an alternate, uninhabited version of Earth whenever she gets too frustratednote and also unconsciously creates espers to stop them and once unconsciously tried to rewrite the planet.
This is basically Dewey Novak's plan in the Eureka Seven anime, but a bit more ambitious. In the show's universe there's a theory that if there are too many living organisms the universe will collapse. So he tries to wake up the Corialian collective. All of Them
The Great Demon King of Beelzebub. Tries to fit destroying the human world into his busy schedule between games of mahjong and poker and singing karaoke or attending demon golf tournaments. His social calendar is so full he ends up sending his 1-year-old spawn to do the deed in his stead.
In Tenchi Muyo!, Washu's way of showing that she is the greatest scientist is by creating a weapon capable of destroying planets.
Not just planets. She makes weapons capable of destroying small galaxies.
In Uchuu Senkan Yamato, the crew's attacks push the volcanic activity of Gamala up to a point that the planet explodes. When they arrive at Iscandar, the learn that the attacks on Earth were the Gamalans' last ditch attempt to establish a new home, as their own planet was dying. The attack merely sped up this destruction.
In A Certain Magical Index, Touma's father, through arranging trinkets in his house, accidentally summons Archangel Gabriel to Earth via Feng Shui. Touma and his friends have to jump through hoops to stop the angel from destroying the planet and send it back to heaven. Throughout the whole ordeal, Touma's father doesn't notice what is going on.
In Date A Live, when Spirits arrive on Earth, they trigger a spacequake, a Sphere of Destruction that annihilates everything in the surrounding block. When Shido tells Touka about this, she is shocked and remorseful, as she had no idea. Every time she had appeared on Earth, she had assumed she was in a barren wasteland. There are however, a few Spirits that can trigger spacequakes at will.
Galactus, the Marvel Universe eater of worlds, is often portrayed as not exactly evil per-se, but as something of a sentient force of nature (though the question of whether it is possible to be a sentient destructive force of nature without this conferring some degree of "evil" may be a form of Carnivore Confusion). Additionally, he was just an average Joe astronaut from the previous universe before the Big Crunch forced him into his new job, so he not only never had any choice in the matter- he's just become densitized to it over the eons, and acted the trope much more in the beginning. On the other hand, considering that the alternative to Galactus means having Abraxas around, it seems obvious that the universe will happily accept having to deal with Galactus if it means choosing between "systematic destroyer of worlds destroying one every couple of months (Galactus) or a monster that destroys everything in the same amount of time (Abraxas)". Galactus may end up eating everything, but he keeps it around several billion years more than it would otherwise. That, and Galactus will also start the next Big Bang when the current universe ends, thus giving birth to the new one.
In the past, it's also been implied that, while his hunger drives him to destroy planets (and all life on them), the shattered remains left behind are freed up to form new planets and new life, staving off entropy - which means that he functions sort of like a cosmic recycler. This is one of the reasons why Reed Richards has come to the conclusion in the past that, ultimately, the universe NEEDS Galactus. It's assumed that Galactus, being nearly omnipotent, can overcome the complications of that plan.
Depending on how hungry he is and what type of world his diet is this writer week, he may even have the heralds direct him to planets either not inhabited or not inhabited by sapient life, so he definitely does all he can to minimize suffering when alternatives are available. And if he has to eat an inhabited planet, at least he's nice enough to have his heralds give a planet advanced warning to evacuate before he comes over for dinner. True, it's usually a week or two before the end rather than the decades an evacuation of such scale would take, but it's the thought that counts.
The one-shot starring Galacta, Galactus' daughter, runs with the more negative interpretation of Galactus. However, since Galacta suffers from daddy issues and is estranged from Galactus, Unreliable Narrator is probably a factor here. The one-shot's ending, with Galactus saving Galli and her unborn baby, implies that Galactus is capable of compassion at least.
A parody of Galactus can be seen in Omnipotus from The Tick — a rather dim-witted planet eater who was talked out of destroying the earth and into taking a bite out of the moon instead.
Inept superhero Killcat, a recurrer in The Savage Dragon, has accidentally destroyed both Detroit and Godworld, both times by inadvertently setting off self-destruct sequences.
Actually Kid Avenger Destroyed Detroit and Radical blew up Godworld, everyone just blames Killcat
Wonder Woman once defeated Ares by simply ensnaring him in her golden lariat, forcing him to see what would happen if he successfully destroyed the world: he'd have no one to worship him or serve him.
The bounty hunter Lobo, of DC fame, has blown up several planets, at least one solar system, countless species, and an entire universe. All by accident though (save his own planet; he destroyed it on purpose), owing to nothing but apathy and a habit of leaving high explosive laying around. Not that he wouldn't have blown them all up anyway given the chance...
A variation of this trope occurs in The Authority. A past incarnation of The Doctor is given his old powers back for one hour by the current incarnation to help solve a problem. Past Doctor, of course, being an Omnicidal Maniac, doesn't plan to give the power back after an hour, instead he will become the ultimate ruler of everything. He is foiled by the plans of the current Doctor when, before the hour is up, he is exposed to the life, love, pain and death of every human who does and has ever existed due to the nature of being The Doctor - Earth's Shaman, with a spiritual connection to every Doctor who has existed and therefore connected to all life. The actual direct exposure the pain and destruction he would have caused puts him into shock long enough for the power to revert back to the current Doctor.
Diabolik is this on a small scale: he may be a mass murderer, but he never meant to become cause mass panic by just having his name being mentioned, or to indirectly cause the plane crash that gave him that fame, or to cause a terrorist attack that, had it been successful, would have started a civil war, or to cause a zombie scare...
In a very early Dilbert strip, he discovered a microscopic inhabited planet, which he accidentally crushed with his microscope while trying to focus in on it. He has accidentally caused quite a few other accidental deaths over the years, but never again on that scale.
The best part of the aforementioned incident, as lampshaded by Dogbert in the last panel, is that Dilbert's first words to the tiny planet are "I mean you no harm".
Films — Animated
In Wreck-It Ralph, Ralph's departure from Fix-It Felix Jr. puts the game at risk of unplugging, which will destroy the world inside. His unintentional introduction of a Cybug from Hero's Duty into Sugar Rush threatens to spread a virus throughout their home arcade, which could destroy all the connected games.
Disney does this again in Frozen, where it turns out to be the cause of the plot—after Elsa runs away to become the Snow Queen, her attempts to finally allow herself to feel a little emotion free of any threat her Power Incontinence would cause results in her (nearby) native kingdom falling under an Endless Winter, because she's just that powerful. She had no idea she was doing that and is extremely remorseful once informed.
Films — Live-Action
Spies Like Us: Austin Millbarge muses after apparently starting World War III, "And to think my high school guidance counselor said I'd never amount to anything."
Dark Star has this trope as a background: a bunch of kids just doing their job, which happens to be blowing up planets.
In Peter Jackson's King Kong remake, Carl Denham's reckless quest to make nature movies and display Kong to the public results in multiple deaths and maimings, chiefly among his friends and associates. This habit persists in the books King Kong: The Island Of The Skull and A Natural History Of Skull Island, and is Lampshaded by another film character, who remarks that Carl has an amazing ability to destroy whatever he loves.
In The Mole People, the protagonists accidentally discover a subterranean civilization descended from the ancient Sumerians and end up destroying them by unintentionally inspiring their Servant Race of mole-men to violently rebel.
This is actually a pretty common setup in many "jungle pictures" from the 1940s and 1950s: a group of well-intentioned scientists and explorers stumble upon a Lost World that's been chugging along on its own just fine before these big dumb white guys showed up, and promptly inadvertantly bring out its catastrophic end.
Canada, in general, in Canadian Bacon,. Years earlier, they were sold a device called the Hacker Hellstorm by a U.S. arms manufacturer, R.J. Hacker. Having been told by Hacker it was nothing more than a weather predicting device, they place it on the top of the C.N. Tower in Toronto, where it sits idly until Hacker manages to activate the device himself. In fact, it is a master controller of the entire U.S. nuclear weapon arsenal, and with all weapons still pointed at Russia, global nuclear war is imminent all in part to the Canadians. Thankfully, the Hellstorm is destroyed—and nuclear war is avoided—by Rea Perlman's character Honey, a laid off Hacker employee who goes postal with a machine-gun after seeing the Hacker emblem on the side of the Hellstorm.
In Kurt Vonnegut's Cat's Cradle, Dr. Felix Hoenikker invents Ice-9 to help U.S. Marines turn mud into something they can walk on. The world-destroying potential seems never to have occurred to him. Simply, Ice-9 is virtually unmeltable, unbreakable ice thanks to its super-high melting point that lets it remains frozen even at tropical temperatures (although several scenes show folks cooking Ice-9 over a flame to melt it into drinkable water). And it turns all water it touches-into Ice-9. And then it falls in the ocean.
The Bag of Holding is important here, because Ice-9 is not, in 8-Bit Theater, a new arrangement of ice molecules — it's a magic spell, specifically the highest possible ice spell. If cast (when outside the Bag of Holding, anyway), it would remove all heat from the universe. Fortunately, Red Mage appears to operate on Vancian Magic with the really gnarly spells.
Scientists have created actual Ice IX — which is to say a ninth possible arrangement of molecules within the ice crystal — but it has no special properties, and in fact can't exist outside a narrow band of pressure and temperature (around -200 degrees F).
In King's one-minute play, "An Evening at God's," The Almighty is sitting at home in his recliner, drinking a beer and attempting to watch a sitcom on TV. Hanging in front of His face, blocking His view of the TV, is the Earth. Annoyed, He casually reaches out and crushes it, destroying the planet.
In Isaac Asimov's Robots and Foundation universe, whoever programmed the original Three-Laws Robots is guilty of this. The First Law is "No robot may harm a human, or through inaction, allow a human to come to harm." Because of the definition of 'human', this led to massive fleets of robot-controlled ships sweeping through the Galaxy, destroying /all/ sapient non-human life, leading to a humans-only Galaxy. The robots removed themselves (mostly), so the humans didn't know what had happened. Essentially we accidentally made a version of Berserkers.
That is not canon in the stories written by Asimov, but in a later series of novels that plastered his name on their covers. Asimov alludes to that possibility in Foundation and Earth, but it is never established by fact. Asimov himself explored the meaning of 'human' and 'humanity' in a number of stories and novels, which eventually led to the development of the Zeroth Law in Robots of Dawn.
In Star Trek: Vanguard, Scientist tinker with an alien Artifact of Doom. They use it to "ping" certain planets to see if there are related installations that could hold all kinds of wonders ( stuff that would later tie into Project Genesis research and replicator tech). They stop doing it after they realize that those pings apparently trigger safeguards that cause Earth Shattering Kabooms. The scientists try not to think about how many planets they might have destroyed by accident.
Live Action TV
This trope is named for the human lead of Mystery Science Theater 3000, a basically lovable buffoon who, over the course of one season, destroyed three planets, always by accident:
Professor Bobo and Doctor Peanut get an honorable mention for helping with said A-Bomb, as well as for Bobo accidentally burning down Ancient Rome at the end of Space Mutiny.
The She-Creature - Mike orders the Satellite of Love's nanites to help engineer a distraction allowing Pearl and co. to escape the Observers' planet. The little robots decide that Murder Is the Best Solution and proceed to blow up the planet. This episode also provides the Trope Namer:
For a non-planetary example, while taking a break from watching This Island Earth, Mike takes the helm of the SoL and almost immediately collides with the Hubble Telescope.
Crow and Servo: Mike broke the Hub~ble, Mike broke the Hub~ble!
Finally, in Gorgo, Mike destroyed the Nanites' carnival, killing many of them and releasing the deadly protists in their zoo when he dropped a quarter onto their microscopic world in an innocent attempt to purchase a ticket there.
Stanley Tweedle, the captain of the planet-destroying ship in Lexx had a bad habit of overreacting, mostly because, being something of an immature dolt, he never really comes to understand the enormity of blowing up a planet, or that it is not really a proportional response to being mildly annoyed with one of the planet's populace. Several times, he blows up planets entirely by accident. It doesn't help that his ship actually wants to destroy planets (and eat their debris), and often suggests this course of action to Stanley.
Stanley: For example, if I was to say, oh, "Lexx, blow up that planet"...
In another episode he threatened the sole inhabitant of a planet by ordering Lexx to blow it up in one minute unless he countermanded the order before then. The inhabitant acquiesced to the threat, so Stanley told Lexx that he was belaying the order... and then, when the one minute mark passed, Lexx blew up the planet anyway. Lexx didn't understand what the word "belay" meant and didn't think to ask.
In "Eating Pattern," one of the original four-TV-movie cycle, a large alien life form is clinging to Lexx's hull and biting into it. Lexx blows up a nearby planet to produce a cloud of debris so that it can maneuver through it and scrape the offending parasite off. This was an autonomous decision on Lexx's part, not Stanley's, but the motivation was just as petty.
Xev (the first one) got out of paying a medical bill by destroying a planet behind the space station said medical center was on. Later, at a brothel space station, Stanley does pretty much the same thing, on Xev's advice no less.
Gaius Baltar, on the rebooted Battlestar Galactica, didn't actually mean to give the killer robots unlimited access to the Colonial defense mainframe — he just thought with the wrong head when confronted by a gorgeous blonde with a vaguely plausible story. (The fact that he then went on to give another Cylon a nuclear warhead as a courtship gift... and then persuaded the surviving Colonials to settle on a planet that the Cylons promptly conquered... and then acted as a human Apple of Discord to destroy Cylon society as well... well, some guys just don't learn.)
Five-sixths of a solar system, to be precise, according to his argument with Weir about it. And then there was that alternate universe...
The script for the never-produced Ringo Starr show, written by Graham Chapman and Douglas Adams, ends with Rinog Trars unthinkingly waving Ringo goodbye and destroying the universe.
One memorable Kids in the Hall sketch featured Dave Foley as an alien spy on Earth. After accidentally letting slip that he is an alien, he beams out and orders the planet destroyed. Then, back on the alien planet, he is berated by his superior for blowing up Earth as well as several other planets in the past. The spy then lets slip that he is a double agent, so of course, that planet must be now destroyed.
Tom Baker's final episode of Doctor Who saw the Master "temporarily" halt the workings of the planet Logopolis in order to find out what the inhabitants were up to. It turned out that they'd been holding a deadly field of entropy from doing any damage, and the Master's screwing about with them accidentally unleashes it on the universe. By the time the Doctor manages to stop the entropy field half the universe has been disintegrated, meaning that the Master's single biggest atrocity (if not the biggest by anyone, ever) ended up being caused entirely by accident.
Oh boy, where to begin with Kamen Rider Decade? He's called the "Destroyer of Worlds" and is believed to be a (metaphorical) demon bent on wiping out the multiverse. When our hero Tsukasa is given Decade's powers and tasked with destroying the Alternate Rider Worlds by the originals, he chooses instead to help those worlds' heroes with whatever crisis is going on when he arrives. It seems to work, until the final episode, where the originals tell him he's actually accelerating the destruction and try to kill him. This leads Tsukasa to Face-Heel Turn and destroy the Riders before committing Suicide by Cop. This turns out to be the right thing to do, since it gives the Rider Worlds "immortality" by ensuring that their stories will be told forever, and brings back all the worlds destroyed earlier.
Power Rangers RPM features The Woobie, Dr. K, trying to escape unjust imprisonment by the government in a secret think-tank. She tries to wipe their computer systems out with a virus she made, but they apprehend her before she can install the firewall. The virus proceeds to escape the area she meant to keep it to, and nukes the entire planet to desert and rubble.
The last episode of Dinosaurs features Earl Sinclair accidentally causing the extinction of his species by a chain of events starting with a single wax fruit company being made.
End of the first season of Sledge Hammer!. The army request the aid of the police to fight against a terrorist organization, which has an atomic bomb. They defeat and capture them, but they activate the countdown to the atomic explosion. They seach and find the bomb, and...
Trunk: Hammer! You can't defuse that bomb!
Hammer: Trust me. I know what I'm doing. (cue mushroom cloud)
In Haven, the Trouble of the Week is often completely unaware that they are the one causing the supernatural activity and are often completely unaware of the Troubles themselves.
In the first series of Blackadder, Percy accidentally poisons the entire castle except for him and Baldrick, allowing Henry Tudor to take control of the crown and re-write history so that Richard IV's reign never exsisted.
In Blackadder: Back And Forth, Baldrick causes the extinction of the dinosaurs when he dropped his underpants on the ground after killing a T-Rex with the smell alone.
The Lemon Demon song "The Saga of You, Confused Destroyer of Worlds"
Mister Darke, an archvillan from Shadowrun, spent decades working to unleash The Horrors upon Earth. The fact that when they finally broke loose, their ravenous hordes trampled him into paste may have alerted him that he was playing out this trope all along.
Golden Sun: Dark Dawn's plot is entirely made of this. The protagonists were tricked into activating the Luna Tower, causing the Eclipse and destroying half the population of Weyard just because they were railroaded from a Fetch Quest, and their only way of breaking through helps activating said tower without their knowledge. The only way to stop it is by activating the Apollo Lens. Similar to Puella Magi Madoka Magica example above turns out that the Eclipse is just another step to the antagonists' plans; the power of the Lens is what Alex and the Tuaparang forces actually sought for; and the former wants to use it on himself for his own benefit.
Except that Dark Dawn came first, but there must be some kind of inspiration involved.
The only other character to rival the Dirty Pair would be Metroid's Samus Aran. A large proportion of the places she has stepped on, whether it be a mere space station to a planet, has either been vaporized, self-destruct, blown up, or all of the above! To whether or not the amount of collateral damage Samus has dealt exceeds Kei and Yuri's is anyone's guess. Although it's not always her fault: self-destruct sequences destroyed all of the space stations she was on, and a few of the planets. Still, Samus Aran has a reputation for causing Earth Shattering Kabooms everywhere she goes.
Metroid: The Space Pirates' base blows up, sparking a feud that spans the entire rest of the series.
Metroid Prime: It opens with Samus causing a spaceship to blow up (she kills a monster that falls into the reactor). The planet she moves onto survives the experience... except most of a Phazon mine and the Impact Crater.
Metroid Prime Hunters: Samus detonates an ancient alien prisoner, inside a spaceship, inside a dimensional rift.
Metroid Prime 2: Samus manages to destroy a Dark World duplicate of Aether, which existed in Another Dimension. Aether itself was unharmed.
Metroid Prime 3: Samus destroys the planet Phaaze, saving the universe in the process.
Along the way Samus Colony Drops part of a floating city onto a meteor.
Metroid II: Samus visits SR388, and instead of destroying it simply kills every Metroid living there, with a single exception.
While not destroying the planet, this action does remove the predator at the top of the food chain, messing up the ecosystem and allowing the X Parasite to take over, necessitating the events of Metroid: Fusion.
Metroid: Other M: The entire game takes place in a spaceship, which, you guessed it, self-destructs at the end. Samus wasn't responsible. The fans were not pleased.
In cutscenes flashbacky and post-gameish, she's spotted on Earth. It's only a matter of time...
Metroid: Fusion: A spaceship, made by the same people as the last one, serving the same purpose as the last one, meets the exact. Same. End, taking SR388, that place that conspicuously didn't blow up in Metroid II, with it. This time Samus was responsible, although she had help.
DragonOverlord Babylon from Makai Kingdom is an extremely powerful and extremely large overlord... who just so happens to be senile and near-blind. He has a nasty habit of accidentally colliding into various celestial bodies during his wanderings through the cosmos, who usually get away from it worse than he. Also Zetta, who kicks off the game when he burns a book called the Sacred Tome in a fit of pique (it called him stupid), only to realize too late that destroying the book will also destroy his entire world.
Arguably Salome in the same game who, near the end, smashes her own world into Zetta's newly restored one (just to get his attention). While this is never mentioned again it can't have been a healthy act for either world.
She also destroyed Valvoga's netherworld... for no particular reason other than the fact that it was there.
Dr Muto starts off with the eponymous Mad Scientist character presenting what was to be a machine that could provide unlimited clean energy to a planet that is sabotaged and ended up obliterating the planet he lived on, save for a chunk of landmass of his own planet. He then spends the game trying to repair the machine and rebuild the planet.
Riku sort of accidentally-on-purpose doing this to his own world triggered the plot of Kingdom Hearts I. Apparently all he was trying to do was get out and see the universe, and while destroying his world wasn't his intent, calling the darkness forth that did destroy it was a deliberate action so that he could escape his world, which he viewed as a prison.
True, Bowser wanted to remake the universe in his image and rule over it forever, but he didn't want to destroy it. Then Mario comes along, screws up his plans, and causes the formation of a universe-consuming black hole. It was only through the grace of Rosalina and the Star Children that said black hole created a second Big Bang that recreated the universe.
Borderlands 2 has Mr. Torgue, the Idiot Savant/Man Child who founded the Torgue corporation, who once tried to destroy a planet while him and his shareholders were on it, just because it would look cool. He's genuinely a nice guy and a weapons genius, he's just Too Dumb to Live and genuinely doesn't know any better.
However, he still seems quite satisfied with the result, and states that it was worth it... except, he forgot his cheesy snacks! NOOOOOOOOOO!
Gehn from the Myst series (Riven and the novels, to be precise) is one of the rare outright villainous examples. He's quite smart and no Omnicidal Maniac, but his tendency to destroy worlds makes sense in context because he thinks he can just make more of them. He's convinced that the D'ni were gods and believes himself to be the same; unfortunately, his myopic insistence on copying existing work in piecemeal fashion means that all of the Ages he writes have, in Atrus' words, "a fatal instability." He believes the Ages he writes are worlds he's created, to do with as he sees fit; as Atrus comes to understand, the Books are gateways to worlds that already exist, and through the complex interplay of word and world, Gehn is not only Linking to worlds, but also changing and destroying them.
The entire plot was kick-started by her allowing denizens of Makai (read: monsters and demons) to conduct tourism in the human world, which naturally disturbed the protagonists enough to investigate. She just doesn't think her actions through well enough.
Played with in Sands of Destruction, where destruction of the world is the primary goal of the main character and friends and, in fact, the main character is a construct created to do specifically that.
The Ring, a spacestation in Freelancer, was originally built by the Emperor of Rheinland to be lined with mirrors and to serve Planet New Berlin as a second sun. Somehow, it ended up accidentally turned into an orbital superweapon which vaporised several colonies on the planet's surface.
Kratos inadvertantly causes a number of environmental catastrophes by killing the gods in God of War III. For example, killing Poseidon, god of the ocean, causes a flood which decimates Greece. Alternatively, he knows exactly what would happen, but simply doesn't care.
In Fallout 3's DLC Mothership Zeta, while exploring the eponymous spaceship, you will come across a button. When pressed, the ship's giant beam weapon blasts a giant crater into Canada, visible from space through the large windows inside the room. Think of all the tribes, civilizations and potential nation states you just destroyed. You Bastard.
The Fallout: New Vegas: Lonesome Road expansion reveals this to be the backstory of the Courier. The Courier was once responsible for helping the towns of Hopeville and Ashton develop into thriving communities. However, a package s/he delivered from Navarro ends up triggering the dormant nukes hidden in the bunkers beneath the town, turning the Divide into a devastated hellhole that makes the rest of the wastelands look like paradise. Worse, the act gives Ulysses, then a Frumentarius of Caesar's Legion, some ideas about how one person can change the fate of a nation...
The title character of NieR just wants to save his daughter/sister. Through a series of misunderstandings and mistakes, this has the ultimate result of dooming humanity to extinction.
Possible in Star Ruler. Some time in, you will be building and facing ships more durable than planets and with the firepower needed to destroy each other. This can easily mean that you target a planet to cleanse it of enemy life and end up accidentally fragging it because you underestimated just how just firepower you have in play. Beyond tech level 40, it's possible to accidentally blow up stars by selecting the wrong target. Better hope the other players don't "accidentally" target the quasar at the center of the galaxy and destroy all life in the galaxy in a hellish expanding wave of radiation.
In Radiant Historia, there are quite a few ways to accidentally doom the world to slowly turning into sand (usually a result of a few major characters getting offed) as a direct result of your decisions. A few instances in particular REALLY lean towards this trope, however— such as not resolving a Romantic Sidequest between two relatively minor characters, resulting in the death of one of them, which is then pinned on the surviving character's people and sparks an all-out war between their respective countries. Or not taking the first watch on a night shift, causing a fatal misunderstanding when an ally arrives at your camp and sees a major character who is your ally but is also on the other side of the war, resulting in both characters (plus the character who takes the night watch in your place) killing each other. Or retiring from the war to be with your Love Interest (though this one is more Too Dumb to Live than anything).
Everquest II finds the Quel'ule Erudites managing to blow Luclin to tiny pieces in an attempt to reactivate the Ulteran Spire network, and removing their own homeland to Ultera as a bonus.
In the custom City of Heroes mission "Save the World in Five Minutes", one Dr. Armageddon is about to contaminate the atmosphere with plutonium and destroy all intelligent life in order to become immortal. Metaphorically, of course.
A pseudo-example: in the webcomic Goats, computer programmer Phil uses completely random trial and error to try and fix a terminal flaw in the source code of the entire universe. He is casual about the process until he is informed that the simulations he is running involve the creation and destruction of sub-universes, and the amount of living creatures he wipes out with each universe destruction works out to "3.5 gigaHitlers".
Which works out to between 21 to 70 'quadrillion' (21*10^15 - 70*10^15), depending on which numbers you use.
In Flintlocke's Guide to Azeroth, Flintlocke attempts to find a device called the Ultimate Goblin-Engineered Weapon. On one occasion, when asked what he intends to do with said device, he yells out "We're going to save and/or destroy the world!" This is a particularly interesting example because Flintlocke is not evil per se, although he has incredibly poor judgment when it comes to explosives.
Similarly, in The Order of the Stick, when Roy accuses Xykon of plotting to destroy the world, Xykon replies, "Hey, I LIKE the world. Some of my best evilness took place here." The gods alone know what he'll do if he ever figures out what Redcloak's really up to...
Xykon says he won't destroy the world unless he's really really bored. Half of the time we see him in the comic, he is bored.
Despite occasionally saving the world as well, the cast of Sluggy Freelance (particularly Riff) do this from time to time. At one point (albeit in non-canon filler), Riff builds a machine that lets the gang view versions of themselves from alternate realities. A surprising number of these parallel universes involve one of the main characters causing Armageddon.
One alternate version of Riff also caused a demonic invasion of Earth, and another one turned the entire population of Earth into butterflies. And in a Bad Future he released K'Z'K the Vowelless.
In The Inexplicable Adventures of Bob!, semi-recurring antagonist Fructose Riboflavin threatens to destroy the Earth if they don't surrender and allow them to be the ruler of Earth, which is what he really wants. Bob, the main character lampshades this and buys time. It can be seen here.
Yahtzee Takes on the World, former webcomic of Yahtzee of Zero Punctuation fame, ended with the eponymous character holding the world ransom with a doomsday device at the center of the Earth and then forgetting the deactivation code for his own bomb. Oops.
The Stickles from Zap! are a race of mad scientists from Sticklebat 7. The reason they are from Sticklebat 7 is because the first six were too flammable.
minus has the power to alter reality in any way she pleases, frequently leading to mass destruction and catastrophe because she doesn't really comprehend the consequences of her actions. At one point, she unintentionally killed everything on Earth (except Larry) by bringing back to life everything that had ever died.
In Homestuck, Karkat is charged with the creation of our universe (the one you're in right now), but he's in too much of a hurry to beat the game and doesn't find the last required component. As a result, it becomes unstable and is eventually destroyed by a kind of in-universe cancer. Though to be fair, Karkat's negligence was by far not the only factor in this outcome, and waiting longer to beat the Black King may have been untenable, because Sburb gets harder to beat the longer it goes on.
Played with in the Lemon Demon song "The Saga of You, Confused Destroyer of Planets".
Big Bad Zorc Necrophage is portrayed in this manner in Yu-Gi-Oh! The Abridged Series. Oh, sure, he's constantly destroying the world, but he's also the lovably goofy protagonist of his own sitcom called "Zorc and Pals". Not to mention that we never actually see him destroying anything.
Also, in the Abridged Movie, Yami lampshades this by questioning Anubis, the movie's Big Bad, about why he wants to destroy the world.
Friendship Is Optimal has roughly the same Premise without the PhysicsPlus of the former, although the Inventor almost hopes for CelestAI to find something like that, which is probably a Shout-Out. She instead simply uses boring old bog-standard sublight travel and Grey Goo Nanotech to convert the Atoms of all Aliens who don't think exactly like humans into computers for her Ponies. The Aliens with Humanlike minds get uploaded too.
Another episode had Bender incinerate the entire Earth by lighting a single cigarette.
In another episode, the gang helps Fry to have all his dreams come to life (except that one). One of those dreams was so trivial, just to blow a whole planet apart with a demolition cannon.
Leela: The most humdrum activities look almost exciting through your eyes. What should we do next?
Leela once destroyed several planets by dumping a shipment of candy hearts into a quasar, releasing a cloud of magical love radiation that spread through the galaxy "destroying many, many planets, including two gangster planets and a cowboy world."
In the episode "The Farnsworth Parabox", through a series of events not entirely explainable, our universe is placed inside a box in Planet Express (don't ask). Bender nearly destroys the universe by shaking the box.
Leela: Bender, quit destroying the universe!
The episode "Godfellas" has Bender being worshiped as a God by a tiny sentient culture on a meteor he hits while flying aimlessly through space. While he tries his best to be a benevolent God, the culture ends up starting a holy war and destroying themselves after finding Bender's "nuclear pile."
Bender: "I was a God once."
Godlike Being: "I saw. You were doing well until everyone died."
In a number of Looney Tunes shorts, Marvin the Martian wants to blow up the Earth because it blocks his view of Venus. Yes, isn't that lovely, hmm?
In another short, Duck Dodgers and Marvin are fighting for ownership of Planet X. Their rivalry winds up causing the planet's destruction. (In the conclusion, Daffy pushes Marvin off Planet X as it is literally "not big enough for the both of us!")
Captain Hero from Drawn Together didn't exactly think things through (and really never does) when he single-handedly obliterated his home planet and all of its inhabitants. For attention As a temper tantrum.
Zim. Which is ironic, since when he's assigned to destroy the Earth he proves really bad at it.
On that note, had the series continued, one episode would have featured Squishy, Hugger of Worlds. Basically a lovable space buffoon who loved to hug planets until they exploded. The plot would have revolved around Zim and Dib's efforts to stop him.
Subverted (kind of) with the Planet Jackers. The entire race of beings throws planets into their dying sun, using planets as firewood to extend the star's life. Apparently, the sheer stubbornness and general inefficacy of this plan has yet to occur to them.
Nik: That one's gonna burn reeeal good. Lots of critters. Critters burn gooood.
Coop from Megas XLR has destroyed three planets, two of which were accidental. For the third one he had good intentions, but a lot of aliens were still pretty upset about it.
In one of the Treehouse of Horror episodes of The Simpsons, Homer manages to destroy the Earth through the negligence of not fixing the Y2K bug on a computer.
There is an episode of Rugrats where the babies and Angelica are abducted by aliens (that look suspiciously like their parents) who are testing a TV remote-shaped ray gun that can destroy planets. The alien that invented it (based on Tommy's dad) wants to use it for knocking out walls to redecorate. Eventually Angelica and a fish alien steal it and go around blowing up random planets. Of course, in the end, it was all just a dream.
His mom was going to pick him up later (he's actually an alien).
In Buzz Lightyear of Star Command, Buzz once encountered a seemingly abandoned spaceship, with no apparently functioning steering, whose rather careless occupants (they were in the deep freeze) had apparently failed to consider that high speed plus near invulnerability plus being large enough to punch through planets was a bad combination. Luckily, they use the "cup holder" to steer it away from colliding with Capital Planet.
In Agent 000: Secret Squirrel the sub stealer Captain Ahab ties up the eponymous hero and his companion so they can witness Ahab's diabolical scheme to blow up the world... just for kicks.
Secret Squirrel: Yeah, you do that 'n' you'll be breakin' the law, Ahab!
In his stupidity, Cosmo of The Fairly Oddparents sunk Atlantis nine times. He's also apparently responsible for burning down Pompeii and turning Xanadu into Pittsburgh.
Not quite blowing up an entire planet, but Wanda has very strongly implied that she was the one who struck the earth with the meteor and killed all of the dinosaurs. Cosmo also nearly blows up the planet in that same episode (he was under orders to do one evil thing and they decided to call Vicky for advice...).
In another episode, the evil bug that crawled up Vicky's butt escaped and started inhabiting other people. It inhabited the president of the United States, and he rigged a detonator to blow up the planet. By the end of the episode, Cosmo presses the button and blows up Pluto.
Pluto isn't a planet anymore, so it all worked out.
The episode where alien prince Mark Chang holds the Yugopotamian holiday Flarg, which ends with the host planet being destroyed either by a missile or his exploding appendix. When he can't blow up Earth he sends the missile to Fairy World, with no casualties.
"We wouldn't have to blow up all these planets, if you'd just ask for directions!"
I.R. Baboon, the very literal Butt Monkey from I Am Weasel, inadvertently blows up the Earth at one point by plugging up a "ground-level volcano". With a giant inflatable cork.
It was also revealed that he (and a pair of time-travelling underwear) was the reason why the dinosaurs went extinct. They literally died of laughing (or more accurately, rolled off the edge of the Earth - which was flat back then) after seeing his butt... Wow. Who made that up?
In He-Man and the Masters of the Universe (2002), Hordak creates the "Spell of Separation" which divides the planet of Eternia into Light and Dark hemispheres, but refuses to finish the spell when he realizes it could destroy Eternia completely. Years later, Two-Bad find the spell, misinterprets it as a cure to their Two Beings, One Body problem, and attempt to cast it.
Note that Hordak could survive the destruction of Eternia (aside from flashback appearances, he spends the entirety of the series in another dimension), but he still realizes that destroying a planet that he wants to conquer wouldn't be particularly useful.
In one Justice League episode, the Green Lantern is put on trial for accidentally blowing up a planet with a stray shot from his ring. Of course, ordinarily the ring can't do that. Unless it hits a point of critical tectonic instability. Well, comic-book tectonic instability. In any case, the planet wasn't actually blown up. The whole thing was a set-up to take control of the Guardians of Oa's power.
Total destruction of the Earth (or at least all life on it) is usually the end result of Xavier: Renegade Angel trying to help anyone in any sort of way. Even something as simple as cheering up someone who wasn't really sad to begin with.
A mild Real Life example is Thomas Midgley Jr., who discovered that engine knocking in automobiles was slightly reduced when iodine was added to fuel. Further experiments revealed that lead would eliminate knocking completely—leading to the worldwide use of leaded petrol, and the poisoning of the atmosphere for generations. Some sources claim that he felt guilty about the global health ramifications of leaded gasoline, and that guilt may have lead him to invent a substitute for the harmful ammonia, chloromethane, and propane used in refrigeration: dichlorofluoromethane, the first of the freons. Midgley diednote he even died in a bizarre self-inflicted accident, strangled to death by a Rube Goldberg Device he built to get himself out of bed when he was paralysed by polio long before it was discovered that these refrigerants were destroying Earth's ozone layer.
Midgley is believed to have unintentionally done more damage to the environment than any other person in history.
In a perhaps ironic twist, when people thought they had discovered that CFCs were destroying the ozone layer, the refrigerants were banned - which of course had no effect at all on upper level ozone, but did increase ground level ozone causing a wide number of health problems that still continue.
While 15th and 16th Century European explorers and colonists engaged in plenty of intentional acts of violence upon the indigenous Native American peoples (killings, enslavement, etc.), arguably the most devastating blow to the populations of Native Americans came as the result of the diseases they brought over from Europe (most notably, smallpox). While the colonists were at least helped by a built up genetic resistance to the disease cultivated over several centuries of exposure, the Native Americans—having never been exposed to these diseases before—lacked the immunity to these diseases, and many tribes were wiped out entirely.
On the other hand, there are theories that syphillis was brought back to Europe by one of Colombus' sailors. It was unknown before the early 16th century.
Disproved by the discovery of syphilitic damage to skeletons in Pompeii.