"A master of the Dim-Mak can poke an enemy in a certain spot and they die. It originated in ancient China when early man still had prominent off-switches located around the body, much like a modern lamp. Back then, you could kill a guy by selling him the wrong sized hat."
Bleach: Soifon's released zanpakuto creates a butterfly print on the body of whoever it hits. When the attack hits the same spot a second time, that person is instantly killed dies after a time period sufficient for them to realize their predicament. What makes this ability even scarier is that the second strike does not need to share the same entry point as the first one; it only needs to share the same surface of the first strike's wound itself. She demonstrates this by impaling Ggio Vega twice, once from the front and once from the back, both times striking the same area in his lung inside his body.
Matsuri's Inherent Gift in Sola is the ability to rapidly decay anything she touches (if she chooses). Takashi freezes in place when she grabs hold of his arm during one of their battles.
Scar's body destruction technique in Fullmetal Alchemist. It's explained as being incomplete alchemy- - alchemy is in three parts, analysis, disintegration, and reintegration; Scar stops at the second step. Edward does the same while fighting the Slasher Brothers.
The title character of AR∀GO: City of London Police's Special Crimes Investigator picked up this ability from a supernatural Serial Killer, but has failed to find a way to turn it off. So far he's not angsting much about it, since it helps him fight other monsters, but it's a bit inconvenient, to say the least. (It's decay-based and works on anything organic, though it's slow-acting enough that he's been on the wrong end of an Armor-Piercing Slapwithout doing any with only minimal damage to the slapper's hand.)
Crocodile arguably has this ability. His touch doesn't cause instant death, but he can dehydrate you pretty quickly. His Ground Death attack, however would likely be a instant kill, as he rapidly dehydrates everything within an Instant Death Radius into sand, from trees to statues.
Darker Than Black: If Hei can touch you (either directly or indirectly with a conductive material), he can electrocute you to death.
November 11 as well, where Hei can essentially fry people he can turn them into popsicles - he can instantly flash-freeze anything he makes contact with.
This isn't a literal example, but if you watch Axis Powers Hetalia, you know that Russiais notto beangered.EVER. All of the countries know this. So when he goes to visit Italy and Romano, he tries to be as sweet as possible, and goes as far as putting his hand on Italy's shoulder. This causes them both to freak out, and Romano's next line could be the Trope Namer. (At least, in the English dub.)
Black Mage Zeref from Fairy Tail has this as his main magic, but he can't really control it, that's why he isolated himself for several centuries.
Laurel Darkhaven of Rising Stars is dismayed at first that she can only use her telekinesis to manipulate small objects. Until she realizes that includes the carotid artery. She becomes an assassin for the government.
Rogue from X-Men is normally Blessed with Suck, but during some issues her sucky power was overloaded into the "you touch her, you'll die" category.
There was also Wither from New Mutants, whose power was decaying any living (or once-living) thing he came into contact with. He eventually left the institute and fell in love with Selene, who was immortal and couldn't be affected by his power.
Another Spider-Man villain with touch of death is Styx who got his powers from cancer experiment done by his associate Stone. He needs to kill in order to survive, can kill almost anything living and can disintegrate organic matter. He almost killed Venom Symbiote with his touch in one of his first fights.
An early issue of Grant Morrisson'sAnimal Man featured the tragic "Red Mask" who'd always wanted to fly. In the 50's he touched a glowing meteor hoping it would give him powers; it did but the power was a literal death touch, any person or animal he touched would die. He feels he has no choice but to become a villain, something he's not very successful at. Animal Man runs into him in the midst of a last hurrah, attacking San Diego with lowtech robots he'd won in a poker game. Now elderly, overweight and dying of cancer he throws himself off a building and Animal Man is too late to save him.
The Touch Of Death is common in the Marvel Universe. Besides Rogue and Wither, there's Selene the former Black Queen of the Hellfire Club, a mutant with a life draining touch who has lived for millenia thanks to her powers, during which she also became a powerful sorceress. One of her followers, Lois London aka Mortis, constantly emits a disruptive energy field that can induce heart attacks in living creatures. X-Force member Joshua Foley aka Elixir can use his bio-manipulation abilities to kill people (pretty horribly too). Dark Young Avengers member Melter can, well, melt anything with a touch, and much like Wither, accidentally killed his parents this way.
Alpha Flight villain Deadly Ernest was an example of both this and The Punishment: as a soldier in World War I, he was killed in battle, but rejected Death when she came for him. As a result, he was cursed to kill every living thing he touched. He ended up using the power to set himself up as a crime boss.
In Batman, the third Clayface, Preston Payne, received the power of melting human flesh into protoplasm with his bare touch. Preston is reluctant to use this ability, but he's wracked with horrible pains and headaches, and his touch momentarily allows him to transfer the sickness to another person. It's been mentioned that he's now on medication to reduce this pain, so any time he feels he needs to relieve his suffering is psychosomatic.
In Green Lantern, a member of the Sinestro Corps, Murr the Melting Man, was an alien scientist mutated in a lab accident into a shambling, mindless being who can melt anything he touches. His teammates make a note to keep their forcefields up when he's around.
The Flash: Wally West learned a death touch technique in one mid-80s annual that was never, ever referenced again.
In issue #398 of Supergirl, Supergirl briefly gains a power that means she kills everything she touches.
This happened because the writers were realising quite how ridiculous and annoying the League of Superpets had become, and it was an easy way to drop bridges on them.
In Epic the Boggans' weapons can deteriorate anything they touch. Mandrake's staff is much more potent, able to fell a tree with one swing.
Kill Bill: Pai Mei's legendary Five Point Palm Exploding Heart Technique, which is used by the Bride on Bill himself.
Eponymous in Kiss of the Dragon, where Jet Li is able to do this by delicately applying a needle to the base of the skull, such that when he removes it, all of the victim's blood will travel to his head and not come out, resulting in an agonizing death as he bleeds out of every orifice in his head.
Iron Monkey's Hin-Hung, Imperial Legate Officer, renegade Shaolin monk and all-around Big Bad of the movie, wields the "King Kong Palm," which allows him to deliver "the Buddha's Hit," which leaves a handprint embedded on the victim and poisons the blood.
In The Men Who Stare at Goats, a move fitting this description supposedly killed China's greatest martial artist - thirty some-odd years after the fact. Lyn believes himself to be affected by this. Presumably the story is based on the "quivering palm" theory of the death of Bruce Lee. (Short version: a martial arts master, angry over Lee revealing martial arts sequences in his films, killed him with a slow-acting deathblow.)
In Osmosis Jones, Big Bad Thrax has a particularly long clawed finger which allows him to kill the other cellular beings he interacts with by simply touching them. Within moments of appearing on-screen, he gently pricks a harmless cell worker who horrifically boils/burns alive from the inside out.
Possibly example: the infamous Avada Kevadra spell in Harry Potter kills (almost) anything the instant it strikes. It also utterly obliterates objects.
To clarify, it's not known whether the spell fulfils the 'minimal effort' criteria. The only wizards absolutely known to have used it (Voldemort, Barty Crouch Junior, Severus Snape and Thorfinne Rowle) are all dark wizards that have presumably practised the spell and are very much in tune with that area of magic. The Cruciatus Curse is not an easy curse for somebody that doesn't 'mean it' and so a similar rule might well apply to the big daddy of the curse world, too.
In the novel Forever After, hingu master Gar Quithnick can inflict all sorts of instant or conditional death or paralysis with a touch (in addition to conventional martial arts). The highest technique of his art is a touch that will kill an opponent when he experiences a moment that defines his life. After using it on a deposed tyrannical despot, Gar informs him that he can live a long life of modesty and humility, or go back to his old ways and die.
In the Larry Niven short story Death By Ecstasy the detective hero uses his "imaginary arm", a form of short-range telekinesis, to stop the Big Bad's heart by reaching inside his body and squeezing.
In his books, Robert Rankin frequently references a supposed martial art called "Dimac", with which one can maim and disfigure opponents with a mere fingertip's pressure.
In the Wild Cards universe, there is a literal example and the slightly different "deadly stare" power of the ace Demise, who can kill by locking eyes with a person for few seconds.
Employed in the first book of the Martial Arts series Jason Striker by Piers Anthony.
Sau'ilahk of The Saga of the Noble Dead is capable of killing humans with a single touch. (Dwarves are somewhat hardier, as he learns to his consternation).
In the second book of Skulduggery Pleasant, Playing With Fire, the villain, Baron Vengeous, has a power that quite fits this: If he looks at people and has the will to, he can make "The body forget everything it ever learned about holding together", in short: explode
The fifth book, Mortal Coil, has the Russian assassin Tesseract, who has a rare ability called Bonebreaker. With it Tesseract can fatally shatter bones with the lightest of touches, but apprently it only works if he's touching the victim with his fingertips.
In The Adversary Cycle book The Touch, the Dat-tay-vao, a healing power, also works in reverse if someone gets in the way of the person with the power, and kills them with one touch.
In the Doctor Who episode "The Shakespeare Code", the Carrionite known as Doomfinger displayed the ability to stop the heart with a single touch... and she really seemed to enjoydoingso.
In the lonelygirl15 episode "Shadow of Death", Emma kills the seeker by running at him. In "Help Us!", LaRezisto explains that trait positives have the power to kill Order members with a touch. This was later revealed to be utter bull.
Subverted in "The Enterprise Incident". Spock supposedly uses the famed Vulcan Death Grip to kill Kirk. Later on, we learn that no such thing exists, and Spock actually hit the captain with a Vulcan Nerve Pinch (which in itself is a milder version of this, capable of dropping almost anyone into unconsciousness in a matter of seconds).
Although the Death Grip does not exist, it is revealed in the episode Journey to Babel that there is a Vulcan instant-kill technique known as tal-shaya, which appears to be a semi-ritual Neck Snap. Historically it was used for the execution of criminals, but Spock's father is suspected of having used it to murder someone.
Played straight in the episode with the holographic assassin-babe that imploded people's cellular structure with a touch. If she says "I am for you", run!
Smallville: "Reaper" featured a man who reduced anybody (including a dog and some vegetables) who made skin contact with him to dust. He couldn't turn it off, but didn't seem to be overly distraught by this, and went around "mercy-killing" people whose suffering he considered to be too great. When he touched Clark Kent, even Clark screamed in pain before knocking him away. When he was finally convinced that his mission was wrong and went into What Have I Done mode, he put his hands together, turning to dust himself, which raises a few questions about how he was able to change his clothes and do other stuff that involves touching his own skin.
Only one hand had this power, because he'd been wearing a Kryptonite bracelet on that wrist when he died. Also, it's suggested that he may have been able to turn it off but found it difficult to do so.
At the end of season two, when all of Azazel's children meet up, they start comparing their powers: super strength, mind control, etc. Then one woman tells Sam to stop angsting about his death visions and says that when she touches people, their hearts stop. This included her girlfriend, apparently.
Demonstrated by the Fourth Horsemen, Death himself during his spectacular introduction. Also, when Dean becomes Death for a day, he kills people simply by touching them.
Angels have a specific form of killing touch, it burns out the victims' eyes and liquefied organs. Works on humans, monsters, and demons.
In Tracker, a fugitive named Tev had the ability to do this to the alien Energy Beings, although it took a lot longer in humans.
Cole: One of his victims was a Cirronian diplomat who did great things. One touch from Tev was all it took.
CSI NY had an episode with a martial artist who killed the victim of the week with a single blow to the back of the neck.
An interesting variant in American Horror Story: Coven, where the wielder of said power, Zoe Benson, has no control over her ability, and it seems to activate on its own immediately after sexual intercourse. The effects seemed to be intense internal hemorrhage all throughout the body, causing blood to escape from the eyes, mouth, ears, nose, and possibly other places.
Earlier versions have a few spells that do this (such as Slay Living, the evil reverse of the 5th-level Raise Dead for clerics), as well as the Quivering Palm ability of the Monk, which allowed the monk to simply will the death of the target for some time afterward. The downside is you can only use it once per week. Thanks a lot, Wizards!
Although Monks in 4th edition have no instant Touch of Death attacks, Quivering Palm returns as a highest-level once-per-day power that does high damage and ongoing damage that gets worse with each failed saving throw.
A demilich, which is a lich only more so, can trap a living creature's soul if they fail a saving throw. What's more, unless it's defeated less than twenty-four hours afterward, the demilich will devour it, rendering the unfortunate victim Deader than Dead. And it can trap up to eight souls per day. Have fun.
There is an Epic Level spell in 3rd edition called Memento Mori. You think that you want someone dead. They die. Nothing else to it. They call it Epic Level magic for a reason.
3.0 and 3.5 editions really love these kinds of abilities. Many "save or die" effects exist in the game. To name a few: Flesh to Stone, Disintegrate (you MIGHT survive, but probably not), Power Word: Kill, Implosion (one target PER ROUND), the special Cleric power for the Death Domain (I believe it's even called Touch of Death), the Vorpal weapon enchantment (decapitates on a failed save), to name a few. There are also numerous Psionic variants which are even more brutal, with Decerebrate (save or get lobotomized) being probably the most straightforward. Some of these are not guaranteed to kill you instantly (even if you fail the save), but you have to be really durable to survive them.
Slightly more balanced is the Enlightened (read: fancy-pants martial artist) ability in Deadlands, the aptly-named Poison Palm. Hucksters have a similar ability. Sykers have a number of variations on this trick, but the one that actually requires touch is called "heartstopper." Then again, Sykers are Bad AssSuper SoldierNinjaIn The Future. (Yeah. Dey gots baggage.)
Warhammer 40,000: Mostly the province of daemons and C'Tan, but psykers have been known to pull it on occasion. By accident, on themselves. And anyone unlucky enough to be anywhere near them.
GURPS: Martial Arts notes that this exists everywhere, 17th century fencers had the botte segrete. The actual dim mak is just a use of the (fortunately cinematic) Pressure Secrets skill or an Innate Attack called "Hand of Death".
Feng Shui doesn't have many fu powers that might qualify as a "Touch of Death" (even Lightning Fist, on a path that includes "Dim Mak" which only ignores armor, mainly does damage that bypasses Toughness), but the prime contender for the title would be Storm of the Tiger, the ultimate technique of the Path of the Healthy Tiger, which you can only get by mastering both the healing and the vengeful paths of the style, and which allows you to spend as much Chi as you want on a barehanded strike that you have just made and do twice that amount of Chi in extra damage.
Ming I's Arm of Darkness. The name should say it all.
Magic: The Gathering the keyword ability "Deathtouch", means any creature dealt any damage by a source with this ability is destroyed no matter how tough it is.
There's also a magic card called Touch of Death. Unfortunately it's a waste of a good name, as the card isn't any good, and is incredibly unlikely to actually kill anything.
Exalted, being the game it is, has a myriad of ways to do this. One of the more painful is the sorcery spell Blood of Boiling Oil; Essence swirls around your hands and coats them red, and the first person you touch has their blood turn to... well, you know.
You can also punch off souls, hurl opponents into a temporary orbit, summon a demon to hurl them into a permanent orbit, dismember them, and kick people's heads off with a sufficiently impressive stunt.
Pokémon: Horn Drill, Fissure, Guillotine, and Sheer Cold (30% Accuracy, but opponent faints instantly if hit).
Dragon Quest VI The Pressure Pointer skill that the Martial Artist vocation learns is a pure example of this. There's also the Poison Needle, available since Dragon Quest III, that can get a one-hit kill if it critically hits (it's extremely weak otherwise).
The Poison Needle's effect actually makes it the safest way to kill Bomb or Crag type enemies. Simply hand it over to a Jester (huge crit range), then have the rest of your party just sit back and have a staring contest with the little bastards till the needle procs.
EverQuest has many bosses that use this as their initial attack. This lead to a rather humorous habit of bringing sacrificial halflings, rangers, et cetera.
Gaia from Grandia is capable of absorbing any living being's life force and consequently petrifying them with nothing but it's presence. The worst part? Gaia is a humongous plant/insect Eldritch Abomination that spreads like wildfire.
The Touch of Death as a spell used by high-level spell casting monsters, and a more potent version by Death himself. Unlike the other versions, this one is unlikely to kill a well-prepared adventurer.
The Wand of Death, which, coupled with an angry gnome, can really ruin your day.
Powerful wizards can learn the finger of death skill (which is what the wand shoots). Anything without resistance is instantly obliterated (including the Wizard of Yendor). Oh, and did I mention it's a ray spell, meaning it can hit multiple targets at once?
Shiki's Magical Eye in Tsukihime allows him to see points of death. Simply poking such point with any sharp pointy object (like a kitchen knife or a sharpened pencil) will not only instantly kill said thing but also terminate its reincarnation cycle and any other metaphysical life functions it may possess. And this power is not limited only to living things, incidentally: he can "kill" non-living things as well. He once cured a person of poisoning by "killing" the poison.
In Worms 4: Mayhem, if you use Prod on an enemy worm during a match where the "Dim Mak" option is selected in the Wormpot, it will instantly kill him.
In World of Warcraft, monks have a skill called Touch of Death that can instantly kill an enemy if it has less health than the monk (though you can't use it on other players for obvious reasons).
Death Touch was a spell used by "Guardians of Blizzard", which were NPCs that served as a Border Patrol for areas players weren't supposed to enter. These have disappeared since Cataclysm unlocked any areas that a player could get to that they previously weren't supposed to.
Any game that uses the Super Star power up, which makes your character invincible and uses Collision Damage to instantly kill enemies by just touching them.
Feng Wei of Tekken practices the particularly brutal (and fictional) God Fist Kenpo style, with one of his unblockable attacks invoking the Dim Mak directly, both by name (Death Palm) and method (being what amounts to a highly ritualized short palm thrust that takes away a massive amount of your health bar).
In Scribblenauts, if you create Death, the game makes a small Grim Reaper which has this power and can kill anything with a touch, including Death and God.
Kid Radd: This is how Collision Damage is portrayed (and what it's called!). Those with it cannot control it, and must avoid touching normal people. (It seems that those with it can touch each other without harm—at least, Bogey can touch other members of his species.)
In How I Killed Your Master, Master Fei tells young Liu Wong that his father's style, aptly named "The Divine Fist of the Unconquerable Sky," used what we can presume are Touches of Death and Paralazyer attacks.
Master Fei: "All he would say of his style was, 'I don't know what it's like to hit a man twice."
Twilight Lady has this as her signature killing technique. It took years to master, but if the target has committed murder of any kind, she can just use her martial arts to poke them to death - or stand still and watch them grope her. Which is why it's surprising when a female muscle demon slaver IS COMPLETELY IMMUNE.
Batman: The Animated Series: The ninja Kyodai Ken discovers this and promptly decides to turn it against our hero. However, the always Crazy-Prepared Batman wears padded armor over the deadly spot (which Batman figured out by looking at which spot hat been hit the most on Kyodai Ken's training dummy) in order to convince the villain that it doesn't work.
Kyodai Ken is apparently killed after their fight, leaving Batman as the only person in the world who knows the Touch of Death, as well as the only person who would never use that knowledge or teach it to anyone else.
Bart claimed to learn the Touch of Death in a karate class he had actually skipped out on. Which he then repeatedly threatened Lisa with to force her to do minor chores. (And was really just the "rock on" sign that he copied from a video game. \m/ - or rather \n/, as this is the Simpsons)
Played straight in a Halloween Special when Homer accidentally killed Death to save Bart. Homer tried on Death's cloak for fun and was conscripted by God to take Death's place. At one point Homer abused his Touch of Death to get better seats at a baseball game by killing everybody in the way. He justified it to Bart by saying they would have died eventually.
Tai Lung is able to paralyze anyone with his nerve strikes, but his method was crude and amateurish compared to Master Oogway who is fast and skilled enough to strike with a complex pattern of nerve strikes and do it in Bullet Time! Also subverted in that one of Po's advantages is that his body fat protects his nerves so well that nerve striking is useless on him.
There's also the Wuxi Finger Grip, which (apparently; neither the scene in question nor Word of God is entirely clear) causes the victim to explode with city-shaking force merely by flexing the pinky finger.
Death from Family Guy can kill with a touch; excused by his being, well, Death. When Death Takes a Holiday and Peter needs to fill in for him, simply wearing Death's shroud causes anything Peter touches to instantly die, even without intending it. He learns this the hard way.
"Note to self, do NOT go go the bathroom".
In Aqua Teen Hunger Force, there's one-shot character Dan from Grim Reaper Gutters, who won't leave until he makes a sale! He kills Carl with a Touch of Death after Carl refuses to buy any gutters.
Timmy Turner's Mom in The Fairly OddParents can never grow anything in her garden, because she believes she is cursed and most forms of produce tend to shrivel up when she touches it.
*bawling* "EVERYTHING I TOUCH DIEEEEES!
Which was then Played for Laughs as his Dad says "Hey Dinkleburg. Why don't you come over here and give my wife a congratulatory hand touch?"
In one episode where Mr. Turner started a farm, it showed he's just as bad, even with the land being magically enchanted to grow.
The Venture Bros.: This is Phantom Limb's super power, aside from having invisible limbs. Apparently he actually can control this power, unlike Marvel Comics' Rogue, as observed when he was able to shake Brock Samson's hand with non-lethal effects. When activating this ability, the veins in his invisible limbs spark and give off a green-red light.
While not as easy as it is in fiction, a strike to the front or back of the neck can kill a person with much less force than anywhere else on the body.
This is commonly referred to as a "Rabbit Punch", and as such is highly illegal in professional combat sports.
Halfway between the above and below examples, a precise strike to the carotid artery can stimulate the vagus nerve, drop the heart rate and blood pressure of the victim and cause immediate unconsciousness. The touch of death part comes from the very real chance of dislodging a cholesterol plaque and causing a stroke.
It's also theoretically possible to kill someone with a very precisely timed blow to the heart during the T-wave (the refractory period), initiating ventricular fibrillation, and effectively stopping the heart in what is known as commotio cordis. The level of precision this would require (plus the knowledge of the human body) makes it extremely difficult to do deliberately.
There have, however, been documented freak cases of children dropping dead from cardiac arrest after being struck in the chest, particularly with a baseball or other sports instrument. Children are particularly susceptible to commotio cordis due to the lack of development in the rib cage. This can also be triggered by lightning strikes.
On the opposite end of real-life touch of death, there is the "precordial thump", which is essentially a desparation move when a defibrillator isn't imminently available. It is done by placing a sharp strike to the center of the chest. It's the same mechanism as commotio cordis, but in reverse. It's usually only attempted once, and only when cardiac arrest is directly witnessed.
While not so much "minimal force", it's possible to kill in one strike via striking the throat as mentioned above.