In the Next-Gen Fic series Legacy, Big Bad Joseph Risdon is seriously pissed off that Team Arrow put him behind bars sixteen years ago, and he intends to make Oliver and Felicity pay by visiting everything he suffered in prison on their children.
How I Became Yours has several instances of this. The first is Zuko discovering that Mai hid evidence of Katara's pregnancy, which he takes as an opportunity to confront her, throw her to the floor and declare he never loved her (which saddens her to the point of crying). Then Katara bloodbends Mai to death because Mai caused her to miscarry. Admittedly, Mai was trying to kill her at the time, but Katara could just as easily have used bloodbending to incapacitate Mai and send her off to trial.
The 'World Financial Crisis Gangbang' comics. I mean, really — was raping America really the best way to sort out the financial crisis?
There has existed at least one fanfic in which Canada brutally tortures or murders another character in response to their heinous crime of not remembering Canada's name. To be fair, that does happen to him a lot.
Old Man Henderson started a personal crusade against the cult of Hastur, eventually resulting in the cult's, the Mad God's, most of his allies, and Old Man Henderson himself's deaths, because he thought the cult stole his lawn gnomes. What really happened was that he sold them and donated the proceeds to charity while high off his ass, and therefore had no memory of the event; once he sobered up he mistakenly assumed they were stolen.
He also plans to "wipe out (Soku's) entire gene pool" for turning him in to the police. For the record, wiping out her gene pool would involve wiping out the entire human race. Apparently, for him, it just means killing her extended family.
After he gets shot in the shoulder after accidentally teleporting to the Super Bowl, he kills 6 million people just to prove a point about how dangerous angry Horteka are.
In "Days of Futures Past What Does That Mean It Kinda Sounds Sexy", Kurama tells Robin that someone once insulted ramen in Naruto's presence, so Naruto retaliated by tying them up to a Prius and throwing the person off a bridge. Kurama doesn't say if the Prius was used to suspend the person off the bridge and dangle them upside down or if Naruto threw the car afterward to help sink that person to the water bed below. Most likely the latter due to the fact that Naruto doesn't like Prius vehicles for some reason.
Death Note Equestria: Twilight, as Kira, kills criminals of various calibers — her main targets are Karma Houdinis and those she considers unrepentant — so a pony with a life-long history of minor offences might also be offed. Second Kira (Fluttershy), meanwhile, openly kills those who speak against Kira.
Loki: Agent of Doomgard : The Loki of Battleworld's Paradise domain would narrate any Loki dead for entering that domain. One walks in then drops dead. No other provocation needed, no questions asked.
The Prayer Warriors often engage in this, particularly by deciding that anyone who disagrees with them deserves to die. One example is Idiosy, for whom hacking into the author's account is cited as an in-universe reason for having Rachael kill him and burn down his house, killing all his wives and guards.
In Renegade, the Global Defense Initative uses this as a basic part of their military doctrine. If someone fucks with a GDI colony, their response is to utterly destroy whoever attacked them with overwhelming force. This doctrine lead to them obliterating the pirate bases at Torfan from orbit, and results in full-scale war with the Batarian Hegemony due to them supporting attacks on human colonies. One Citadel politician accuses GDI of "making an example" out of the batarians, which GDI pretty much agrees with.
In The Story To End All Stories, the villain was forgotten by the rest of fiction, so he decided to deal with his frustration by kickstarting the Apocalypse.
Murder is shown as a very rare and serious crime in Equestria, and the punishment for the guilty is banishment... to the Moonor the Sun. After hearing this, Phoenix immediately takes it as going too far.
Then there's Trixie, who took the job as the prosecutor as an opportunity to get revenge on Twilight and the mane 6 in general for revealing her as a fraud. Although it's implied later that that is not Trixie's main reason for wanting to get back at Twilight, as indicated by the presence of black psyche-locks when asked about it.
For defying their prophecy and "embarrassing" the Powers The Be, Xander Harris is sentenced to be sent to a world without life in Hellmouth Trooper. Fortunately, someone else steps in and instead he's sent to Kamino.
In Tricksters and Gods, Loki (resurrected as Harry Potter) is a big fan of this:
After realizing that Ginny stole the diary in book 2 (and worse, has a crush on him!) he assaults her, carving "Thief" on to her back, and warns her that he will ruin her entire family financially if she doesn't leave him alone.
After Voldemort's resurrection, he immediately assumes that Dumbledore plans to martyr him and runs away. Years later, he dismantles the entire wizarding world, imprisoning, institutionalizing, and/or bankrupting various families, most of whom had probably never even spoken to Dumbledore.
In Things Unseen, Things Unknown, and Things Yet to Be, Xander questions Willow's decision to keep an employee whom she knows full well is spying on them. Willow responds by cutting him off from all Council resources while he's on a mission to an area that's already cost them six people. In other words, she's risks the death of a friend she's known for roughly forty years because he disagreed with her.
Volt reveals in Conquering Eostia that the reason he's raised an army to take over the titular continent and turn all its women int Sex Slaves is because his band of mercenaries were sent on a Suicide Mission by one of the kingdoms to defeat another kingdom. Naruto agrees with Volt's desire for revenge on the people who hired him, but can't justify such horrific extremes and vows to stop his former comrade.
Most of the main cast in Dragon Age: The Crown of Thorns, and some others, feel that the DN protagonist lashes out at Isolde a bit too strongly, although, true enough, she did outright accuse him that he doesn't mind killing children. Basically, he makes her cry with "The Reason You Suck" Speech and even deliberately makes her think he is going to/did kill Connor. Fortunately, he'd only gone upstairs to give the kid a hug and a So Proud of You, plus talk to the demon possessing him face to face.
When Connor is finally exorcized, the DN gets quite angry at Alim's impersonation of the Grim Reaper and, instead of congratulating him and whatnot, drags the mage over to give him a What the Hell, Hero?? rant in private. Alim counters it by calling him out on how he reacted too harshly, showing off his own Guile Hero traits by perceiving one of Raonar's biggest regrets.
A rewrittenversion of Chapter 372 where Erza responds to being stripped naked, having your sensitivity to pain heightened, and then getting whipped like crazy and electrocuted by chopping Kyouka's arms off, smashing her face against a stone floor multiple times, ripping open her stomach and leaving her organs exposed, ripping out a few of her organs, including one of her LUNGS!, squashing her shoulder bones like tin cans, more electrocution, and horrifficly ripping out Kyouka's eyes! Jesus! Even as payback for Cold-Blooded Torture, this is overkill!
In Shinra High and Shinra SOLDIER, Julia and Sephiroth are big fans of this. In response to being attacked by half the football team (even though the football players lost spectacularly), Julia and Sephiroth get revenge by blowing up the football field during a game, openly wounding players and spectators in the process.
During the Wutai arc, Julia tortures both her victims due to minor slights. Gorki, for daring to call Sephiroth a woman, is tortured until she screams, which includes cutting off both her arms and crushing her legs with Demi. Staniv breaks Julia's katana, so Julia paralyzes her, cuts out her eyeball and forces her to eat it, and then mutilates her so she can bleed to death.
Gavin Caine opposed Tracey's campaign to investigate whether Millborough being built on a former nuclear test site had an adverse effect on the population. Why? To get back at his son Anthony through Tracey and her husband Gordon, first for Anthony working for them instead of him, then for opposing his expansion plans for being outdated.
Kortney Krelbutz wanted revenge on Moira and Elly, the former for firing her, the latter for not hiring her back. (Never mind that she was busted stealing.) She steals Elly's husband John from her (not that she ever knew, given her untimely death), inherited his millions when he died, then used that to buy out the store she was fired from and fire Moira in turn, then bought out most of Millborough to have it absorbed into Greater Scarborough.
When Renny, a young Slytherin, gets caught with a copy of the Quibbler in his bag, he gets his arms broken by Crabbe and Goyle for being a "blood traitor." Then his dad pulls him out of the school. Then Voldemort murders him along with his whole family. Renny's story was one of the greatest Tear Jerker moments in the fic.
Remember in Harry Potter and the Goblet of Fire when Ron and Harry were having an argument, because Ron was feeling Overshadowed by Awesome and he felt Harry was hiding something from him? Well, Rose Potter of The Girl Who Lived responded to this by throwing Ron around the room and carving words into his forehead.
In My Immortal, "Samoro" (allegedly James Potter) and "Lucian" (allegedly Lucius Malfoy) are in a band together. Lucian plays a few wrong notes during a concert, and Samoro responds by attempting to shoot off Lucian's arm. But it was later revealed that Snap(e) used Demonic Possession on Samoro to make him do the above, meaning this trope is subverted.
Not to mention when Ebony's friend Willow becomes a 'prep', she is then murdered and her body is dumped in the woods. And is raped by 'Loopin', because he's a 'necphilak'.
When Ebony and Britney have a confrontation, Britney makes a few off-hand remarks and mocks Enoby. What does Ebony do in response? Use a curse to torture her.
Granted, Britney didfree Snap, Loopin, and Hargrid from "Azkabian."
A more extreme example: When Ebony and "Satan" are making out while taking each others' clothes off and someone tells them that they can't do that (since they're watching a movie in public), Ebony drains her blood.
Interestingly, though, the author seems to try to justify the murder, claiming beforehand that the woman was a prep out of nowhere.
Belinda Jabez in Tom Riddle's Schooldays wants to kill Jana Teires for making the Gryffindor Quidditch team when Belinda herself didn't make the Slytherin one.
In The Real Us, Blaise calls Hermione a mudblood. His punishment? Being dropped on his head hard enough to be knocked unconscious, imprisoned for a week, and denied any medical treatment during that timenote He almost certainly has a concussion, not to mention potential neck injuries!
Hitman Miami: In one of the chapters, it is mentioned that should 47 even trip off a metal detector, an army of guards will shoot him to death, "as is standard procedure in the event someone sets off a metal detector, anywhere, in the entire world." (This parodies the All Crimes Are Equal trope from the original games.)
The Bombshell has a double whammy. The protagonist Ada has a...thing about being touched. In kindergarten, she recalls, a little girl surprise hugged her from behind and wouldn't let go. So she kicked her. Then, in response, every student in school shunned her for eight or so years. Those kids really know how to hold a grudge.
A rather brutal example occurs in The Kids Who Cried 'Ouch', an answer fanfic to the episode "The Boy Who Cried Gorilla." In the fanfic, Ryan, Connie, and Renee get their "just desserts" for their initial treatment of Richie when he first sees the gorilla. Among other things, Ryan gets beaten to the point that he suffers a drug addiction that causes his grades to fall to flunking levels, Connie gets a knife up the vagina rendering her sterile, and Renee winds up repeatedly getting raped to the point that she winds up pregnant and ends up suffering a miscarriage.
Don't take Ryuuko's toys or else. To elaborate, Nui took Ryuuko's stuffed rabbit and Ryuuko's response, rather than tell on her, was to threaten her with an AK-47.
In Cellar Secrets, the reason as to why Ryuuko was locked away in a cellar and underwent horrible abuse is surmised as "because she was born". Of course, whether or not that was the actual reason she was locked away has yet to be said, but that is all Satsuki and Nui have to go on. As we later found out, this was part of it, as a mentally ill Ragyo had become pregnant with her just as her marriage had collapsed.
In The Day Everything Changed, the main antagonist of the story, Sakura Takahashi, went on the attack, giving Kagami the mother of all beatdowns and injuring the poor girl so badly that she had to be rushed to the hospital. What the hell did Kagami do to deserve this? The fact that she simply scored higher than Sakura on a midterm (and considering Sakura has been held back twice, and got a 36 while Kagami got a 96, she should have realized this would happen). If that's not Disproportionate Retribution, then I don't know what is. It doesn't help that she had secretly had a grudge towards Kagami for god knows how long. Luckily, justice quickly catches up with her.
In With The Old Out With The New: Kano kidnaps Cassie in retaliation following his defeat at the hands of Sonya. Cassie then challenges Kano to kombat for her freedom... and wins. Kano, being the sore loser that he is, rapes Cassie.
However, Kano gets it worse in Mortal Kombat: Redemption, as it is Cassie herself who not only kills his lieutenants (and framing the Red Dragon), but also brutally tortures Kano as payback for kidnapping both her and Jacqui (seen in the Tie-in Comics), before killing him by performing the 'blood eagle'. Then, to make sure he's dead, Cassie blows off the back of his head with a shotgun.
Cadance Of Cloudsdale: Lady Prisimia was banished from Equestria because her boyfriend grew bored of her and started spreading Malicious Slander so intense that Celestia herself exiled her. Actually a Subversion, as Cadance notes how Prismia was under the spell of an evil amulet that amplified the negative traits of her personality and altered her perceptions of reality. It was far more likely that Prismia grew increasingly scathing and hostile until a real incident happened, and she chose self-exile than stay any longer in Canterlot.
Same with Prismia's reasons for stealing love from everyone in Reduit. Because of her nasty breakup with her coltfriend, she decided to take love from these people "because they didn't deserve to be happy" while she was miserable.
Celestia VS Cleverbot: Luna gets upset with Cleverbot and takes out her anger by destroying the computer and setting it on fire.
In Denuo Fortuna, one pony feels up Icefang... ...So she responds by breaking both of his forehooves later that night.
Getting Back on Your Hooves: Why is Checker Monarch so intent on destroying Trixie's life? Because, when she was a filly, she beat her at chess.
In the Lunaverse story At the Grand Galloping Gala, Night Light blocks the sending of emergency funds to Ponyville just to punish Trixie for insulting Twilight. And it gets worse: he tells Trixie the only two ways he'll accept her apology are if she resigns from the Night Court, giving up her life dream in the process, or if she finds and returns Twilight to him. Failure to do either will result in him preventing her from advancing past Representative.
Titan got his face disfigured in his past and was shunned by everyone for his hideous looks afterwards. Years later, he kills his entire species and starts to destroy parts of the multiverse for no other reason than that it is fun. His former fiancee, Serpentari, also has a similar motive.
The author wrote the entire fanfic, which insults bronies as being losers who dare to believe in positive things, because one single brony made fun of him.
In the sequel, he makes Cadance suffer, just because he does not like the fact that in the show, she got happily married.
Ace Ray gets sent to an insane asylum and essentially brainwashed into liking Star Fleet, for the crime of... saying mean things about them. Sure, he beat up his sister, but the way it's worded, it sounds like Starfleet was looking for an excuse to arrest him.
Frosteye had been trapped in a frozen cavern for a century by Princess Celestia due to being a mocker.
Hey kids, is the nerd asking questions that the teacher holds off recess to answer? That's not cool! Let's trick her into going into a forest full of hungry monsters to an ancient and quite possibly cursed ruin where she'll get mind raped by memories she didn't know she had! Sound harsh? In Past Sins, Diamond Tiara and Silver Spoon did it! Although, to be fair, they didn't know that the mind rape thing would happen. The monsters, on the other hand, are common knowledge.
One conclusion to the My Little Pony: Friendship Is MagicDark Fic "Pattycakes"note which, to be fair, is intended as parody ends with Fluttershy singing to Rainbow Dash about how Dashnote who does have a bad habit of saying things without thinking first will never hurt anyone's feelings again now that she's been mentally regressed to an infant. The other conclusion has Scootaloo fail to grasp Fluttershy's philosophy after going through the series of (twisted) tests, and if she fails the final test by drinking water instead of milk, she's regressed even further than Dash (Dash had Baby Talk, Scoot loses the power of speech entirely), with no hope of ever recovering. (For your daily humour-so-dark-light-cannot-escape-its-surface needs, her cutie mark takes the form of a baby's pacifier, since she's not exactly going to have the chance to demonstrate any other talents, now is she?)
When Diamond Tiara went through her mother's jewelry and "borrowed" a tiara (earning her cutie mark in the process), her mother didn't take it well. And by that I mean she tried to strangle her own daughter to death.
Let's not forget the Dark World arc, where Nightmare Eclipse/Paradox, formerly Twilight Sparkle, has been rewinding time simply to continue to make Discord suffer. An interesting example, because Discord really did enough to her to warrant a truly horrific punishment, Paradox managed to go so far, her revenge went into this trope despite how much Discord did to her.
In Sophistication And Betrayal, Cashmere wants to ruin Rarity and destroy her business, simply because the latter declined her affections.
In Bride Of Discord, Discord claims turning Equestria into a World Gone Mad, overthrowing Celestia, and tormenting all of pony kind for who knows how long, was initially just because Celestia got mad at him for several pranks that were his fault. Possibly a subversion, as he was ridiculed and shunned by everypony except Celestia prior, so the only pony who gave him a chance getting mad at him for what he considered harmless fun, may have just been the straw that broke the camels back.
Invoked in Escape From The Hokage's Hat. The council want to banish Naruto, want Sasuke's prison sentence forgotten and were smart enough to get the Daimyo to agree with any of their decisions. Tsunade's response? Shove Sasuke in one of the darkest ANBU cells being kept barely alive, setting up the collapse of Konoha's economy, taking money from the accounts of every clan that ever wronged Naruto and finally making Jiraiya (temporary) Sixth Hokage while she leaves with Shizune, Hinata and Naruto for a six month training trip. When she explains why she did it to Naruto, she has this to say:
"I decided to teach those meddling old fools a lesson in respect. If the reason I came back to the village is kicked out, I am SO joining in the fun!"
I Am NOT Going Through Puberty Again!! has Tobi mutilate a delivery ninja who was delivering his invitation to the Uchiha family reunion. He also immolates the remains and empties his bladder on the body for good measure. Why? It was for mentioning his real name.
Rinne no Naruto has Naruto decide to torture and kill a kid who used to bully him.
This Bites!: In retaliation for the humiliation he suffered on the SBS, Garp forges Sengoku's signature so Merry, an anthropomorphic ship, gets a bounty for chomping on his ass, and Cross and Soundbite get one of the highest bounties in the world. The latter two alternate between being elated and depressed over this, as while this measure of infamy garners a lot of respect and fear, it also increases the amount of enemies and danger they face.
In Latias' Journey, the Ghost King proposes to Latias after sending her several gifts. She refuses his advances, so he kills her family, and then destoys her home, Altomare, along with everyone in it. Judging by the city it is based on, he killed upwards of 800,000 people. Strangely enough, she still falls in love with him.
In New World, Maddie smacks Ashton in the face. And he proceeds to savagely beat her. Keep in mind that the reason she hit him in the first place was because he was tring to rape her.
In the Hans Von Hozel story Pikachus Umbrella, Pikachu is locked in a prison cell for all eternity for stealing a TV set.
In the Poké Wars series, Ho-Oh sees genocide as a fitting punishment for humanity's "enslavement" of Pokémon.
Broggen and his friend Brigger used to be quite fond of drinking, and after consuming too much wine, they go around terrorizing several goodbeasts, ruining Urthblood's chance of gaining the region's trust. Urthblood responds by throwing them into a bog to slowly drown (although Broggen was saved before he perished).
Wolfrum is accidentally pricked in the behind by a young hedgehog's spikes. He responds by taking out his sword, ready to seriously injury (if not kill) the hedgehog.
In a flashback, Benrath and a friend of his spy on his father as he soils himself in his sleep. When Log-a-Log wakes up and finds the two laughing at him, he beats his son to a pulp and then snaps his friend's neck.
In Book I, Benrath humiliates Jurlick by beating him senseless in front of his friends and then defecating into his mouth. While it's understandable for Jurlick to seek revenge, his method of getting back at Benrath in Book II is to directly (or indirectly) kill his three closest friends and then manipulate Rowgat and several monitor lizards into gang-raping him.
Inverted in With Strings Attached. Because the four are Actual Pacifists, when they are treated very badly (even tortured in a way) by the Uneasy Alliance in Ehndrisï¿½at one point, part of George's soul is taken from him and have a chance to get some of their own back, they just slap people around for a few seconds. The worst that happens is a few people get slammed into a wall or hosed down, and George does cat tornado on Brox's head.
It's even more disproportionate when you realize that George did nothing else during the final battle except try not to get hurt, and Paul did nothing except absorb damage and hold Kerrun upside-down and tap her head on the floor to keep her from concentrating.
In Saki After Story, by the author of The Day Everything Changed, Saki narrowly wins against Teru in the finals of the mahjong tournament. When Saki approaches Teru after the match, and Teru beats her up badly enough to send her to the hospital (doing the same to Nodoka when she tries to help Saki), the people covering the tournament assume that it's because Teru is a Sore Loser. It's actually because Saki tried to talk to Teru and claimed to be her sister, which still counts.
In Episode 61 of Sonic X: Dark Chaos, Sonic and his friends heavily damage Beelzebub's prototype flagship. His response? In episode 67, Beelzebub brutally tortures Cosmo and nearly rapes Chris to death after luring them to his base. Although revenge wasn't the onlyreason...
Done to a wicked extent in Prison Island Break. In this prison your protagonists are being tortured, raped, and beaten up almost daily. But they're murderers, psychopaths and serial rapists. The writer never lets you forget it. They deserve it, right? And yet you're feeling sorry for them? Are you sick or something?! Don't worry; there's nothing wrong with your empathy circuits. That conflict of emotions you're getting? That's intentional. You have to feel it to believe it.
In Mr Krabs Unquenchable Blood Lust, when Mr. Krabs learns that the health inspector is a fake posing as a real inspector in order to scam people for free food, instead of calling the police and having him arrested, he kills him with a poisoned Krabby Patty (Although to be fair, this is something he tries to do in the show).
The End of Ends pulls a massive one. The villain, Count Logan, who is Beast Boy after getting a Superpowered Evil Side, sucks people who were mean to him or otherwise were just living happy lives into his book and kills them. He also has his minions blow up Tamaran because Starfire got together with Robin when Terra didn't get together with him. In fact, the entire reason why he was blowing up the universe was because he got "dumped" by Terra.
In Joker's Wild, the Joker kidnaps Beast Boy and puts him through horrific Cold-Blooded Torture for weeks on end. Why? Because an action figure of Beast Boy just happened to be programmed to say "Dude, I'm the King of Jokers!"
In Gensokyo 20XXII Ran was scalded with some kind of liquid (hinted at to be either acid or very hot water) for snooping through papers and was left with severe burns, resulting scars after she healed. That is a pure testament to how brutal their captors are.
In 20XXV,in chapter 66, we have it where Paintbrush Bitch lets Reimu outside of the apartment building, knowing that would place her in danger, which it does when she goes into The Forbiddens, all because Yukari curb-stomped her for calling her a whore.
Arguably, this is case when Reimu stabs Yume Ni with a pair of scissors in response to being kicked in the face, then again, one could say it was an eye for an eye, since Yu dealt her injury and she dealt it back.
Yuuka is virtually the queen of this in Imperfect Metamorphosis, along with being Wicked Cultured. She only lashes out when someone breaks etiquette. An example being when she killed the couple in the hotel room, because they screamed in terror upon seeing her instead of giving her a proper greeting. Another example being that she didn't attack any of Yukari's backup teams until they attacked her, thus breaking the rules of her engagement with Yukari. Kanako picks up on this and manages to talk Yuuka into going home for the day.
One tiny piece of artwork describes Makari, Warlord Ghazghkull mag Uruk Thraka's banner carrier, as his one and only genuine friend. You do happen to remember Ghazghkull's crusade to unite the whole Orkoid race and wipe out Humanity, before clearing out everyone else? That's because he hates them for murdering his lucky Gretchin. In the story written for the artwork, Ghazghkull orders his WAAAGH! to occasionally return to the world where Makari's grave is buried. He then goes to the grave alone and just talks to Makari about his WAAAGH's process. So far, he is succeeding.