Kenshiro, the big-eyebrowed hero, is in the habit of making bad guys' heads explode by poking them with his finger. He often heightens the effect by ceremonially cracking his knuckles first. In this case it's all a matter of where you poke them.
Let's not forget Shin and his favorite execution method: effortlessly pushing a single finger directly through a man's chest. This is how Kenshiro got his scars.
Rei doesn't poke people to death, but he does nearly the same thing by slashing men in half with his fingertips. He is (somehow) able to create a cutting force at his finger's edges. His style happens to be related to Shin's, which is why they both have bare hands able to cut stuff they normally wouldn't.
Yuda, whose Nanto style is related Rei's and Shin's, actually topped them: he usually does the slashing people in half with his fingertips thing, but he once slashed in perfectly symmetrical halves an henchman who had completed his job by poking the air in front of said henchman. The cut started from the back.
Raoh's version is the probably the most brutal — which is saying something, considering how violent the series is. Namely, he dooms Rei by striking a point on his chest with a single finger, causing the character in question to die a slow, agonizing death over the course of three long days.
There's Mercenary Tao killing the one-time Dragon of the Red Ribbon Army with only his tongue (don't ask).
Freeza blowing up a henchman and a very wide area by only blinking.
Vegeta demonstrating his newfound power killing his once rival Kiwi by essentially pointing at him... the list goes on...
The very first Fingerpoke of Doom in the entire series belongs to Goku: when competing with Oolong (who was turned into a mecha) over breaking a stack of bricks, Goku breaks the stack... with his index finger. At age twelve.
The best example being where Nappa and Vegeta land on Earth, and, to cement their status as powerful enemies, Nappa blows up an entire city, by only lifting two fingers, and somewhat casually at that (an attack later monikered Giant Storm).
There's also the Punching Machine in the Majin Buu Saga, where the heroes show world-record-breaking strength, by casually jabbing the punch machine. Vegeta, who does not bother with this the first time around, shows why they had to do that. (Hint: You're trying not to break the machine.)
Used to demonstrate the results of Son Goku's Training from Hell all the way back in Dragon Ball. In the "Strongest Under the Heavens" Tournament, his first opponent is a massive wrestler. He nips between his legs and playfully taps him on the leg with a finger... which knocks him out of the ring.
Also used when Future Trunks first shows up, and challenges Goku to see how strong he is. As Trunks is swinging away with his sword, Goku effortlessly parries each strike with his index finger.
Also, Future Trunks killing Frieza with his sword in about ten seconds, doing what Goku had spent about fifty episodes trying to do, with zero effort.
And then there's Frieza forming and unleashing an all-encompassing supernova that destroys Goku's father, Planet Vegeta, all Saiyans minus four (eight, if the Dragon Ball movies and specials are counted), and a good horde of his own soldiers... all the while sitting and laughing in his hover-chair, using only his index finger.
In fact, Frieza, specially in his comparatively overwhelmingly strong first and final forms, does most of his business this way. The most striking one is when he points at Gohan, Vegeta kicks Gohan out of where he was standing, and next thing seen, is that the mountain that stood a long way behind Gohan had been replaced with a mushroom cloud. Then there's his signature Death Beam, a thin, needle-sharp laser fired from his index finger that can cut a nice neat hole straight through people, specifically Vegeta and Piccolo.
Beers from the latest film, Battle of Gods, sends Super Saiyan 3 Goku flying by flicking him in the forehead, and later knocks out Vegeta with a Tap on the Head.
Seras from Hellsing politely demonstrated the fact that she was a vampire to Pip Bernadette by poking and flicking him during their first meeting. Being a vampire in the Hellsing universe means you have Super Strength, and being poked by a vampire as a mere human is quite damaging.
Shunsui performs this on Chad during the Soul Society arc, after batting aside his enemies' first attack and dodging the rest whilst drinking. When Chad tries to keep fighting despite the difference in their strength, Shunsui draws his swords to cut him down.
Aizen blocks an attack by bankai-state Ichigo with a single finger. It's part of the reason fans refer to him as Captain Superman.
To a lesser extent, Ulqiuorra seems bored in almost all of his fights and even puts less effort in all his fights than the stronger Espada. It's explained later, as he's meant to be a kind of avatar of nihilism. In his fight with Ichigo, he blocks Ichigo's Getsuga with just one hand. Hilarity Ensues (sort of) when Ichigo goes into Resureccion Mode and blocks Ulquiorra's strongest attack with one hand.
Isshin flicks Aizen through several buildings by basically giving him the finger in chapter 398.
Anime-only villain Jin Kariya is capable of completely immobilizing enemies simply by pressing his finger on their foreheads.
Yammy attacks Orihime in chapter 192 with this trope.
Soifon's Shikai is almost like a dart that's worn on her finger. Two hits in the exact same location, and the target will instantly die.
Bazz-B has fire-based powers and he's strong that he can melt Hitsugaya's ice with just a finger. He also inflicts him a fatal wound with two fingers while creating a big explosion.
It may have been a filler, but scary all the same: There's two massive escaped prisoners who can practically shrug off being held by both a bulked-up guy, physical shadows, and even mind control by using just sheer muscle. Tsunade shows up, and these two cower; she then does the same finger-flick to launch them a fair distance and they scamper back to prison. Cue a priceless amazed expression from Ino-Shika-Chou...
In one episode of the anime, Tsunade literally breaks the ground into little tiny pieces by simply tapping it with her heel!
Kakashi has a literalFinger Poke of Doom with his taijutsu technique, One Thousand Years of Death/Pain.
The Hyuga clan's Jyuuken (Gentle Fist) Style consists solely of this, being based on seemingly weak attacks that do no external damage and instead target the internal organs directly, such as when Hiashi killed a Kumo-nin kidnapper with a simple jab at the heart. There's no training to toughen up the inside of your body.
The Third Raikage: Hell Stab: Four-Finger Crossbeam Hand!
The Juubi flicked away a fully-powered Tailed Beast Bomb with one finger.
Like Roy Mustang, who can create huge fireballs just by snapping his fingers. His gloves are made of a material that, when rubbed together, acts like a match on abrasive, thus requiring the motion to get a spark he can manipulate.
Father taking away the ability of people to perform alchemy simply by stamping his foot. Not to mention firing gigantic energy blasts by tapping his finger once he obtains God.
In the 2003 series, a Finger Poke Of Doom was used by the deranged State Alchemist Kimblee to give Scar his eponymous injury.
And of course, taken quite literally with Lust. Her nickname of "Ultimate Spear" comes from her ability to extend and retract her Absurdly Sharp Fingers to incredible lengths in less than a second. In the first anime, she can use the ability to fool a crowd into thinking someone was shot.
At the very end of the series, we know that Yahiko has become a certified badass since he's become capable of blocking a blade with two fingers. Note that this overlaps somewhat with Barehanded Blade Block, but is much more badass, and is likely to generate an Oh Crap response from the one about to get their ass handed to them.
And let's not forget Sano's original entrance in the manga. He enters a bar brawl with someone twice his size, and knocks him flying several feet by flicking him in the forehead.
There's also the fingerpoke version of the Futae no Kawami, which can shatter rocks (and everything else).
When Sensui's "true" personality, Shinobu, arrives, the first thing he does is shake Yusuke's hand... which snaps his arm in two.
Yusuke gets one himself later, when two fighters charge at him and he blocks their flurry of attacks using one finger each.
Also, Younger Toguro gets a lot of these, showing that he had strength beyond any of the characters thus far. The best example was when he took off the whole top half of a corrupt businessman's head by flicking him.
Satan from Shina Dark does this to the first Hero group that shows up. He stops the mages by feeding them in mid battle and proceeds to flick the swordsman in the middle of the forehead. Which of course sends said swordsman spiraling through the air.
The "Bakusai Tenketsu" (or Breaking Point) technique. Ryōga learns this technique which lets him poke his finger into an object — even solid rock — and make it explode into thousands of little shards. Until he discovered that it only worked on rocks — the technique was designed for work in quarries, but can be re-purposed for Nigh-Invulnerability training — Ranma was afraid that he'd be shattered by Ryōga.
Cologne can also use this move. In fact, in the anime at least, she's also shown to be able to use it on steel (she catches a falling I-beam on the tip of her staff after landing in a construction sight, causing it to disintegrate) and wood. In a lesser version of this trope, she's also implied to have a number of Pressure Point techniques with nasty effects; she's shown to have a move that renders the victim so sensitive to heat that tepid water feels boiling hot, and where might Shampoo have learned the Xi Fa Xiang Gao technique from?
Speaking of Shampoo, she also knows a lesser version of the Bakusai Tenketsu... which explodes the content of take-out boxes by jabbing a fingertip at the box.
Ryōga destroys wood too in the manga arc where he and Ranma become babies.
In the first anime adaptation of Maho Sensei Negima, Negima!, Action Girl Ku Fei demonstrates her bookcase-destroying forehead flick, or "dekopin", in the Library Island mini-arc, much to the horror of the other girls. Ninja classmate Kaede can do it too.
In the manga, Jack Rakan accidentally blows up a mountain. After that, Negi is understandably freaked out by the prospect of having to fight him. And rightly so. During the fight, Jack actually uses the mountain-destroying attack on Negi. Ouch.
At the end of the Kyoto Arc, Evangeline shows up to save the heroes from a giant demon by blasting it with a superpowerful spell... which she activates by snapping her fingers.
Also when Chachamaru repeatedly flicks Negi to interfere with his spellcasting. Or pulls his face into funny faces or pokes him or... well anyway, she doesn't like outright violence much. Also, the point was to keep Negi from casting, as each attack breaks his concentration. This illustrates just how weak a spellcaster is without a partner.
Negi himself did this to Sextum, destroying her barrier... and her clothes.
There's a very weird symbiosis with Giving Someone the Pointer Finger: Ryukai's Spirit Attack allows him to control a person's body from a distance, just by pointing at them. Another example closer to this trope is when one of Chinmi's mentors teaches him how to focus his qi into his fingertips, enough to flip off a bear.
Earlier, Chinmi also ran into a hitman enemy whose specialty is finger-poking one's pressure point to the point of stunning the enemy. Chinmi got his ass kicked because of it, but eventually managed to come up with the counter by learning to make his body Made of Iron.
Mewtwo. At the beginning of Pokémon: The First Movie, he opens his eyes, shattering the containment unit he was in, after listening to the scientists. He becomes enraged as he is just an experiment, so he clenches his fists and thus destroys the entire laboratory he and the scientists are in. He then finishes the job by turning his head three times. Other examples: Nonchalantly waving his hand to create a deadly storm, blasting a Gyarados and its Trainer to the opposite wall by raising his arm, and releasing Nurse Joy by snapping his fingers.
There's also the anime episode "A Marathon Rivalry", where Team Rocket is able to take down Ash's Staraptor by using mechanical hands hidden in the balloon's basket to poke it repeatedly and forcefully until Staraptor fainted.
As early as the third episode, after Team Rocket defeats two of his Pokémon, Ash tries to attack the pair himself. After holding him At Arm's Length, James beats him with a flick of his finger.
Digimon Adventure: Myotismon doesn't even need to poke. He can, among other things, block a head-on charge from a Digimon the same level as him and about five times his size by pointing at him. Similarly, there is an instance where he repels multiple projectile-based attacks (which were launched from several Digimon simultaneously) just by blowing at them.
Once he gets a bit of a rein on his anger, Durarara!!'s Shizuo Heiwajima starts responding to mildly annoying people by merely flicking them in the forehead (as opposed to his previous method of sending them flying over a city block). Of course, with Shizuo being Shizuo, this still feels to the victims like someone smacked them in the face with a baseball bat.
Fate/Zero's Iskander casually flicks Waver on the forehead whenever he wishes to dismiss him, knocking him back several feet.
Gaou, who raises a bruise on the opposing team's quarterback by managing to reach him with his little finger. The bruise is about two inches in diameter.
Then Mr. Don appears, and he managed to put Gaou out of commission with one strike. While weakened.
A Certain Magical Index: Accelerator's ability to control vectors lets him pulverize objects as hard as concrete or metal by lightly touching it. The same can be applied to humans...
Tsukune Aono's "sensing supernatural energy" lesson in Rosario + Vampire puts him on the receiving end of one of these from Inner Moka.
Tsukune: (eyes closed) What's this...? I closed my eyes and sense some kind of glow in front of me. I can feel it...! And... It's coming closer! What could it... (opens eyes; Inner Moka is standing in front of him, fingers poised) ...be... Moka: (tropes) Tsukune: (colliding with the white background on the other end of the panel) Urrrrgh!
In Kill la Kill, Nui Harime is so absurdly powerful that she can casually destroy a Goku Uniform with her pinky. Goku Uniforms are made of Life Fibers, which are supposed to be nigh-indestructible except against the Scissor Blade and other special swords.
Watchmen: Dr. Manhattan. At one point teleports an entire mob of people with barely any effort at all. Even more impressive is that he teleported each of them to their homes. At the same time.
In one Marvel Universe fight between Thor and Iron Man, it took five pages and about 20 seconds of in-universe time for the fight to be over. However, the Spit You to Death, similar to this trope, came when Iron Man flew straight at him with great speed, and Thor simply stuck out his hammer, not even flinching as Tony was deflected into some power lines.
During the Mr. Fixit storyline, the Grey Hulk (almost as strong as green, as smart as Banner, and totally amoral) gave a human opponent "da Finger". A finger thump to the forhead knocking him out.
While it happened off-panel, later during the Merged Hulk period he says to the Punisher, "If I had used two fingers instead of one, you'd still be out cold."
In one issue of Spider-Man, a near death Dr Octopus was contemplating all the injuries he'd received over the years, most of which involved getting decked by Spider-Man, but one seen of the flashback montage showed Mr. Fixit casually flicking Dr Octopus with one finger. Doc Ock's comment during that panel suggested it was one of the worst injuries he'd ever received.
In Firebreather, Duncan gets revenge on a bully by breaking his nose by flicking a ball away with his finger during phys ed.
Spider-Man once defeated dimwitted villain The Walrus with a flick of his fingers. To be fair, Spidey was showing off in front of TV cameras because the Walrus had humiliated him earlier, sucker-punching him while he was helpless because of laughter, after hearing that:
The Walrus: Yeah, well — Don't underestimate ME, pal! For your information, I've got the proportionate speed, strength and agility of a WALRUS!
This is Miles Morales', the second Ultimate Spiderman's, specialty. He has a time-delayed stunning power that works by touch, which he usually uses by poking his enemy with his index and middle finger. It tends to be pretty humorous because Miles will switch from trading blows with a super-powered villain to suddenly and delicately touching him with two fingers and watching him have a seizure.
Used in the Uncle Scrooge comic "Cash Flow" after the Beagle Boys have been zapped by an anti-friction ray and an anti-inertia ray — one flick from his fingers sends them sliding all the way back to the prison.
When Thanos was in possession of the Infinity Gauntlet, he was able to erase half the sentient life in the universe by snapping his fingers...which isn't all that easy in the first place, you try snapping your fingers with gloves on!
He also does this in effect to each of the individual heroes(and Dr. Doom) sent to distract & occupy him in the main battle, shrinking the Hulk, turning Wolverine's adamantium skeleton to "spongy rubber", smashing Thor into glass, etc. Perrenial Butt Monkey Quasar doesn't even get an attack in before his patented Quantum Bands are exploded while making an unfulfilled Badass Boast.
To their credit though, each of the heroes' attacks would have been a Killing Blow on anyone else...and is said so in the comic(when else have you actually *seen* Wolverine graphically stab someone through the chest in full view of the camera?).
Thanos finally casually flicks Captain America, the last man standing in The Infinity Gauntlet, with his wrist after destroying his shield, saying: "What have I been doing? Must have been out of my mind..."
The Savage Dragon. The hero kills a bad guy by biting off his finger and spitting it through the evil man's brain.
DC Comics vampires can somehow burst a man's jugular by a snap of the fingers.
It can be real doom if Superman isn't careful. During a fight with the Weaponsmaster he becomes ill. He warns his opponent that due to being rattled from illness a casual blow could shatter a villain's skull.
Quoth Bamse to two gorillas he just had made fly across a jungle clearing: "I just poked you with a finger. Now please calm down, or I'll have to poke you with two fingers''."
In the New 52 book detailing the origin of the Justice League, Batman and Green Lantern have found some alien technology left by a parademon. Superman is the only alien they know of, so they go to Metropolis to question him. Having been in a battle, he thinks they are enemies and fights them, so GL calls in his buddy the Flash to help. While dodging all of Superman's punches, Flash is boasting that he's never been touched. But the next swing barely misses, and Flash suddenly looks worried - then Superman extends his index finger, flicking Flash. Next panel, Flash is on the other side of the block.
He actually hit me. Ow.
Kiden Nixon of NYX has time manipulation powers that effectively give her Super Speed (it's complicated: Time in her bubble flows normally from her perspective and she's able to move normally, but everything else slows down. She doesn't need to eat or sleep, but her hair grows at its normal rate, and when she spent half a year in her "accelerated" state, only a few days passed for everyone else). Even light contact with another person can break bones or cause serious injury (lightly poking her high school bully, Hector's, arm in such a state snapped it like a twig). In the finale she was tempted to see what actually hauling off and slugging the Big Bad with her full strength could do, but declined the opportunity to save her teacher from falling to her death. Considering what she did to Hector with just a poke, it probably wouldn't have been pretty.
In Hulk Vs., Loki unleashes the Hulk from Bruce Banner by lightly "bitch slapping" Banner, which is powerful enough to throw Banner across the room. Justified since Loki's a god and Banner's a physical weakling.
As he enters Jabba's palace, Luke waves his hand backwards and chokes two Gamorrean guards in Return of the Jedi.
Yoda gets one too: In Revenge of the Sith, he enters Palpatine's throne room, and the two Imperial Guards move to stop him. Yoda casually waves his hand backwards and they are thrown against the wall hard enough to instantly knock them out.
At the beginning of X2, Pyro winks in order to turn a zippo flame into something that can engulf a man's arm.
Magneto often does that kind of things during the course of the three movies. Most notably when at one point he send police cars flying around by essentialy raising his hand.
Sebastian Shaw in First Class has this as a secondary ability - he absorbs energy from any attacks, then releases it into anyone he likes with a slight touch. Usually with a kablooey. In his final fight, he knocks Magneto around the room several times by tapping him.
Neo as The One from The Matrix series can stop a hail of bullets simply by raising his hand.
By the end of the film Kung Fu Hustle, the hero is capable of displaying examples of this trope.
Mac has a Love Touch that works at close contact or from a distance in Earth Girls Are Easy. It is potent enough to pull up latent gay tendencies, and to make a man fall in love with a cat he loathed.
In Hancock, the title character manages to destroy a locomotive and derail a freight train merely by leaning into it slightly.
In The Presidio, Sean Connery is such a Badass that he subdues a large biker dude with just his left thumb. The right one would have been just too much. He actually uses both thumbs, and his foot. He was still fighting a guy twice his size while in a uniform not designed for ease of movement.
Parodied multiple times in Kung Pow! Enter The Fist. At one point, The Chosen One throws a punch that stops just short of the boards held out for him — which he then blows away by extending his index finger. In the same sequence he performs pushups progressively with one hand, one finger, and breathing. As the narrator remarks, "Give me some of what he's smoking!"
In one of the Heralds of Valdemar books, this is played with when a very powerful mage knows he could quiet a raging storm from the comfort of his chair with a few little hand motions, but opts to go the dramatic route, complete with flinging open the shutters and waving grandiosely, because he knows that the lesser mage watching him will be more impressed.
The Discworld'sDeath usually gets the effect he wants with a snap of his skeletal fingers. Occasionally he gestures or waves a hand, but he's no show-off. Except when the narrative requires it for a CMOA.
Miles Vorkosigan demonstrates the power of a single finger to Super Soldier Taura, by having her use just one finger to turn up the temperature settings on Baron Ryoval's genetic sample storage freezers, from deep freeze, to the "sterilize for cleaning" setting.
Miles: And the lesson is, it's not how much force you use. It's where you apply it.
In Kamen Rider 555, villain Kitazaki is not only a badass fighter, but also has the ability to turn everything and everyone he touches into ash.
Sylar from Heroes is fond of this. At one point he stands right in the path of an armored truck, and flicks his fingers. It flips spectacularly end over end. Not to mention his preferred method of stealing powers: pointing his finger to slice their skull open with telekinesis.
Elliott from Scrubs once sent J.D. across the room just by poking him, demonstrating that she has the finger strength of a rock-climbing jazz pianist.
Q from Star Trek usually preface their godlike powers with something innocuous like a snap of the fingers or a random shaking of a hand.
The Vulcan nerve pinch. To be fair, it looks easy when Spock does it, but Vulcans are ~3x as strong as humans.
Happy Days: What couldn't Fonzie do with a snap of his fingers?
In the Doctor Who serial Survival, Sergeant Patterson is constantly banging on about his self-defence classes, and at one point calls after the Doctor: "One finger can be a deadly weapon!" Later on, the Doctor subdues him by tapping his forehead with, yes, one finger.
Deliberately invoked by Michael Weston for the cover identity "Louis" in Burn Notice. Sure, it takes advance planning and careful timing, but when he blows stuff up with a finger snap, he goes from kook in a fancy suit to terrifying quasi-supernatural figure.
In The Avengers episode "The Positive Negative Man", just a touch from the villain's finger can literally knock a person through a wall. Of course, he's electrically charged.
Played with in an episode of The Monkees when Peter seemingly knocks out the bad guys by "shooting" at them with his finger. They really just happened to pass out at the exact moment Peter did that (from a drugged drink), but because it's The Monkees, it could have made perfect (non)sense even without the drink.
In Lois and Clark, Superman gets into a boxing match with a bio-engineered fighter. The fighter actually manages to hurt Superman with a barrage of punches, but Superman answers back with a finger-flick to the fighter's forehead, which knocks him out.
The trope namer comes from the January 4, 1999 episode ofWCW Monday Nitro. Kevin Nash — former Hulk Hogan lackey, leader of the nWo Wolfpac, and current WCW World Heavyweight Champion — calls out the (allegedly) retired Hogan after Goldberg (Nash's scheduled challenger for the WCW Championship) is arrested earlier in the evening, and offers to put his belt on the line. Hogan (still ostensibly the leader of the nWo "Black and White" group) answers the challenge and comes down to the ring, the two have a tense staredown... and Hogan pokes Nash in the chest with his finger. Nash goes down like he'd been hit by a shotgun blast, and Hogan covers him for three. Hogan's the WCW Champion again, the nWo is whole once more, and the last six months of storylines are completely reversed — which drove many of the fans nuts. Fingerpoke of Doom have since had strong negative connotations in Professional Wrestling.
According to Dave Meltzer, the whole thing was part of a backstage "work" between Hogan and Nash where Nash would bury Hogan to the other wrestlers (who, like the viewerbase, were seeing Hogan as a Creator's Pet) to get him credibility backstage for taking over as booker, and in return Nash would lay down for Hogan.
The WWF Raw Is War that aired that night was pretaped. Tony Schiavone – on orders from JerkassBad BossEric Bischoff – exposed that Mick Foley was going to win the WWF World Heavyweight Championship that night, on the assumption that knowing the results ahead of time would keep fans from tuning over to WWF. Instead, the fans flocked over to RAW because they wanted to see the popular Foley win the title. WCW's ratings never recovered. Following the Fingerpoke of Doom match, color commentators Bobby "The Brain" Heenan and Larry Zbyszko – both of them heel-leaning announcers – seemed legitimately confused as to what they thought was supposed to have happened, all while Schiavone (the face of the group) never missed a beat in describing the chaos in the ring.
Also Foley won the title at the end of RAW, roughly at 11 PM. The FPOD happened immediately after this, since Nitro ran for five minutes longer. So it ended up being that the fans saw their crowd favorite, Mick, win the title in one promotion, then immediately switched over to watch one of the craziest things to ever happen in a wrestling ring. It was largely considered an Epic Fail of planning that convinced many that WCW was already dying, if not dead. It also is the first example on the Hoist By His Own Petard/Professional Wrestling page.
The above overshadows what is arguably the original "Fingerpoke of Doom" when Shawn Michaels dropped the European title to Triple H during the December of 1997. It normally gets a pass for two reasons: 1. They had something that somewhat resembled a match and 2. It wasn't for the biggest title of the company. The fact that it didn't make several months' worth of storyline moot and played it up like the joke that it was probably helped as well.
Santino Marella's Cobra, jabbing his fingers into the opponent's throat, often while wearing a cobra puppet on his hand.
In Vampire: The Masquerade, there was actually a special Discipline ability for high-level Potence users called Flick, where with a casual touch — a flick, a nudge, a gentle push — you could send someone flying. It was noted to be useful in Elysiums where the rules against Discipline use were a bit lax, as it would be quite humiliating for the target.
In Vampire: The Requiem, the Spina bloodline has access to Courtoise, a power that, at high levels, allows them to inflict damage just by insulting the target.
While spontaneous magic in Mage: The Awakening requires nothing but willpower, rote spells have special hand symbols called mudras that are required when cast. A casual tap on the nose might be the mudra for setting you on fire.
In Rifts cyborgs can have a small laser installed int their pinky that does 1 point of Mega damage. This is enough to kill anyone who isn't wearing armor, though admittedly, so is a stiff breeze in that game.
The monk class, starting at Level 15, has the Quivering Palm class feature. It's a harmless touch attack that makes the victim drop dead if the monk wills it at any time within a certain time frame.
In Scion, this effect is created by the Epic Strength knack "Making It Look Easy."
The Champions splatbook The Ultimate Brick, which explores the wonderful world of Super Strength and how to use it, features two of these. One, the "Finger-Flick to the Forehead", is a massive attack that is limited to non-lethal damage, and guaranteed to render any non-Nigh Invulnerable foe unconscious. The second, named coincidentally the "Finger-Poke of Doom", is rather more messy, and consists of the super-strong character literally ramming one of his fingers into the chest of his opponent as if it were a knife blade.
Godhand employs this trope with the Poke of God, although you'll need to whittle an enemy's health to near nothing for it to work. Still, it can even make demons explode. Specifically, this move can ONLY be peformed on demons, WHEN they have only a sliver of life left, AND they are in dizzy status. So, technically, yes, any other move would kill them at this point too. On the other hand, the Poke of God is a guaranteed instant death attack and gives invulnerability frames like any other reaction command, so it's actually probably the best move to use IF you have somehow fulfilled the criteria for using it. The criteria for using it make the move generally Awesome, but Impractical, though.
Subverted occasionally in Worms: the "Prod" attack is reserved for the most humiliating defeats of all. (It deals no damage, and is reserved for pushing enemies off the edge of a cliff - something that most other weapons can do anyway.) But can also be modified in the weapons editor to force enemies through the sky with 100% damage in some games (Armageddon for example).
Super Smash Bros. has a few instances of this. Jigglypuff possesses an attack called "Rest", which at first appears to be Exactly What It Says on the Tin, sending Jigglypuff to sleep and rendering it inert for several seconds. However, if initiated while the center of Jigglypuff's body is touching another character, it is an extremely potent attack.
Peach can pull up turnips to throw around at things. Most of these are about effective a weapon as one would expect turnips to be. Occasionally, however, she will pull up an extremely potent turnip, or yet more rarely, a Bob-omb or a Beam Sword.
Luigi's taunt, one of the few damaging ones in the game, does exactly 1% damage, with him doing a slow, bashful kick to the ground that knocks someone a fixed distance into the air, regardless of damage. If using it on someone holding onto a ledge, however, it becomes a potent (if impractical) Meteor Move. If otherwise combined with his FinalSmash, not only is the target helpless to react, but it will knock out just about anyone at very low percentages of damage.
One of Master Hand's moves is a literal finger poke of doom. Granted, the finger in question is abnormally large.
Each class in Team Fortress 2 has several seemingly harmless taunt moves, at least one of which causes instant death if it's aimed perfectly. The Pyro, for example, can do a mini-Kamehame Hadoken, producing a tiny fireball, which incinerates you if you're right in front of him (but otherwise does nothing). The Heavy has a literal Fingerpoke Of Doom: by miming a Quick Draw shot with his fingers, he can make an enemy drop dead from a good distance away.
Another example could be the Spy's butterfly knife, which is the weakest default melee weapon... unless you are attacking from behind, in which case it gives an instant kill.
In the final battle of Persona 3 the main character, after being blasted repeatedly with the very essence of Death, heals himself with The Power of Friendship and raises his index finger to seal away the physical incarnation of the end of the world.
Let's not forget Persona4. The main character defeats Izanami-no-Okami by summoning Izanagi-no-Okami — her HUSBAND! How does he do this? After crushing his tarot card, he raises a single finger. When Izanagi-no-Okami appears, he simply points at Izanami-no-Okami. Everything dies.
Normally, Sakura has the Cherry Tapping version this as her taunt: depending on the game, it may or may not be able to defeat her opponent, but it's able to damage them regardless. It's best used during Custom Combos, where it can actually hit the enemy multiple times. However, EX 3 extends this move into an actual Finger Poke of Doom, costing 3 super levels and causing her to leisurely skip towards the opponent and point and laugh at them... causing them to be blasted across the screen and lose most of their health if it connects, in addition to it being unblockable.
Chun-Li's taunt, her bowing and extending her hand, if performed in X-Men vs Street Fighter and if her hand touches her opponent, sends them flying across the screen. Very little damage is done, less than with a jab, but it's still over the top.
Gen's entire punch specials and supers are of the pressure point variety.
In Marvel vs. Capcom 3, Galactus' method of forcing you to switch characters (the Snap Back move) is flicking your current fighter away with one of his fingers, when he's not zapping Power Cosmic at you with a fierce point.
In every game from V onward, you may encounter a creature known as a Tonberry. Aside from its unusually high HP, it seems utterly pitiful at first. It's small and (by monster standards) adorable. Its weapon of choice is a kitchen knife, in a universe where ridiculously large swords and deadly magic spells are the norm. On top of all that, it's slow; it must spend several turns at the beginning of battle just walking up to you before it can attack (the vast majority of foes can attack right away). So naturally, the first time a player ever encounters one, they may assume that it's a joke enemy, and pummel away with melee attacks. And then, the Tonberry reaches your Lightning Bruiser main hero, thrusts its cute little knife at his leg once... and said hero dies instantly. Needless to say, every player learns to take this little guyvery seriously after that. Oh, but it gets worse. Rarely is the Tonberry the most deadly and tenacious monster in the game; that honor goes to its upgraded versions, the Don Tonberry / Tonberry King. You may wet your pants in fear now.
K' and Kula from The King of Fighters series have an attack where they stick out one finger and then clench a fist, the good ol' Bruce Lee One Inch. If it connects, it can throw the opponent so hard they bounce off the far edge of the screen (depending on what the opponent was doing when they got hit).
In Valkyrie Profile, mages in the party can only perform actions once every few turns until their CT/Mana/etc return. You can eventually allocate skill points to a technique called "wait reaction" which allows them a weak attack until they recharge. The attack is from a puny bird (or mini-dragon for the wizards). No enemy can withstand the attack of this bird. It doesn't do much damage, but it is unblockable, causes the enemy to flinch, and leaves them wide open for every warrior in the group to unleash a world of pain. Even the bipedal zombie dragon warrior who can block almost all physical attacks unless you actively attempt to break it will not block it.
Happens in Asura's Wrath, with the final phase of the first boss trying to do this to Asura. Said boss is bigger than planet Earth, and his finger is the size of Tennessee. Itfails.
Happens again in a flashback where Asura has sent one of the elephant Gohma flying towards Augus: he just smirks and flicks it away with his finger with his arms crossed, reducing it to A Twinkle in the Sky.
In the Doom games, lower enemies can sometimes be gibbed with melee attacks, even without the Berserk item.
In the first Halo, simply being tapped by a vehicle at any speed caused instant death.
In the the Gears of War 3DLC "RAAM's Shadow", players controlling General RAAM can direct his Kryll shield with a point of a finger and turn enemy Gears into a fine, bloody paste. There's even an achievement called "Finger of Doom" if you kill fifty Gears with your Kryll.
Fist Of The North Star Kens Rage makes Fudoh a playable character in its Updated Re-release, with moves focusing on his Stout Strength. One of his best moves is an unblockable Limit Break which amounts to flicking a person in the face and sending them sailing across the room. This works on everyone. Yes, this means Fudoh may casually send any of the setting's many badasses sailing into the distance with a flick of his finger, and they're going to be feeling it when he does so. He even gives a jolly laugh while performing the attack.
In the various Tekken games, most incarnations of Jack have had a move called Dark Cutter, which when performed causes him to take three steps forward before tapping the opponent on the forehead with his index finger. It's unblockable and among his harder hitting attacks (though it's so slow and obvious it's Cool, but Inefficient).
In Keychain of Creation, renegade Deathknight Secret apparently does have an affinity for the Water Dragon Style martial art, as illustrated by the gory results of her poking a pig carcass with her finger.
Toph usually does something like this by stamping her foot.
Bumi can also do some decent bending with only his chin.
Ozai can generate lightning pretty much instantaneously, whereas other firebenders are shown to spend several seconds charging it up first.
In a non-bending example, though it wasn't exactly a formidable opponent, Aang was once in a fight where he soundly thrashed his attacker with a polite expression on his face, and the only physical contact was with his butt.
In one episode of Darkwing Duck, an alien villain is an expert at "Galvarin galactic digit fighting", which is thumb-wrestling raised to the level of a martial art.
In the animated adaption of Dilbert, Dilbert attended a security guard training class, and was about to learn how to harm someone with only a thumb. He find this hard to believe, but then his teacher convinces that it is possible, when he accidently hurt himself with his thumb.
The transformed totem characters fling each other across the horizon with casual pokes. Hell, Batman (Man-Bat?) disintegrates a huge mystic boat with a lazy tap.
In the "The Power of Shazam!", this happens twice. After stealing Captain Marvel's power, a villain shows off by knocking Batman to the ground with a flick of his fingers. When the villain loses his power soon after, Captain Marvel does the same trick.
Superman loves this: he occasionally knocks people out with only a flick of his finger. In Justice League he did it to Grodd at the end of "Secret Society", knocking him across a football stadium. He did the same thing to Ten in "Wild Cards".
The "Secret Society" flick, pictured above, also adds a little Crap Under the Radar since Superman uses his middle finger to do it.
In the Batman: The Animated Series episode "Day of the Samurai" Batman travels to Japan to prevent Kyoudai Ken from learning a secret martial art where a person can kill with one blow. Said technique is the core memory touch, where the martial artist pokes someone in the chest and kills them instantly. Batman only survives the encounter by studying Kyoudai's practice dummy, finding the spot that has been poked repeatedly, and adding an armor plate beneath his suit.
It's possible for something like this to happen in real life if you get hit in the right spot at the right angle with even a little bit of force. Doing so will compress the medula oblongata and result in a knock out.
An expert martial artist can break bricks bare-handed. Then can also make strong men cry by poking them.
Carotid massage is a simple procedure where an individual massages over the carotid sinus in the neck, causing a drop in blood pressure as the arteries relax. This is done very gently for five seconds. The physiology is a bit beyond TV Tropes. Urban legend says doing this bilaterally can cause almost anyone to die from cardiac problems, but most people will have no adverse effects. A few individuals may faint or collapse if this is done to them. And a tiny fraction of the population can suffer asystole, or "flatline." Do not experiment on this one.
Antimatter: A few grams of antimater would release an amount of energy comparable to nuclear bombs when coming into contact with normal matter. Which is the reason why there has never been any observation of more than a few particles for fractions of a second.
Bruce Lee gave many demonstrations of a One Inch Punch, which is Exactly What It Says on the Tin. He would have a volunteer stand near him, fully extend his arm to place his fist one inch away from the volunteer's chest, and knock the volunteer completely off his feet with a simple turn of his body.