Whenever Kouji Kabuto of Mazinger Z said this sentence, you knew he was REAL angry, and someone was going to be summarily trashed in the near future. A good example was in the manga, after he learnt Dr. Hell had created a weapon that was able to nullify gravity... and had tested it on an entire city. Another two memorable instances happened in the Mazinkaiser movie (Mazinkaiser vs Great General of Darkness: at the beginning, after Lori and Loru's Heroic Sacrifice, and at the end, right before he absolutely destroys the Mykene empire army:
Kouji: Because of you... Many people have died... THAT IS UNFORGIVABLE! 
This sentence was also used fairly often by Baron Ashura (to Kouji and his friends after being defeated) and Dr. Hell (to Ashura after his servant botched still another operation).
Other Senshi also use it as well, specially Rei/Mars (a Monster of the Week destroys her song sheets she worked so hard to write so she could be in her School Festival) and Ami/Mercury (another Monster of the Week uses babies as hostages, not allowing Moon and the others to attack her) in the R season.
A particularly effective one of these was uttered by Makoto/Jupiter, just before destroying Falion with her Supreme Thunder attack.
A baddie also uses this; namely, Nehellenia in the penultimate story arc in the anime, when Galaxia tricks her into unleashing a nightmare by repeatedly muttering "Unforgivable" until a mirror appears from her heart. She then shatters it, unleashing a curse onto Tokyo.
Haruka in Noein once she really starts getting pissed at the villain. It took the entire series for her to get to this point, and she had been accepting of nearly everyone else's Jerkassness.
Goku of Dragon Ball Z generally delivers this line to villains who went too far with Kicking The Dog, but tends to forget about it before the fight is even over (both Vegeta and Frieza were allowed to leave alive).
The Frieza example was more of a case of Cruel Mercy on Goku's part (considering Frieza was Half the Man He Used to Be at this point courtesy of his own energy disc), followed by blasting him to hell when Frieza made the mistake of trying to blast Goku In the Back as he was trying to leave (though Frieza did get better).
Taken to the next level in the last fight of the Cell Games arc. Cell went out of his way to make sure Gohan was well and truly pissed off, finally killing the Gentle Giant Android 16, to let out Gohan's whole power. Itworked.
Also happened earlier in Dragon Ball when Tambourine killed Krillin. Unlike Goku's later "This Is Unforgivable" moments, Goku actually kills Tambourine purely for revenge.
This results in Piccolo subsequently invoking the trope.
Chichiri of Fushigi Yuugi, rarely angry, furiously unloads this statement on a group of warriors who are about to disgrace an ally's sacrifice. Wisely, they back down.
Used in Naruto during the Retrieve Sasuke arc. Jirobo made the mistake of insulting Shikamaru, then fighting Choji, who considers him his best friend. He shouts the trope and wins the fight. Seriously, don't ever insult Choji's friends.
Tsunade says this to the six paths of Pain after they level Konoha.
Naruto himself is also clearly thinking this during the fight with Pain. However, the Fourth happens to partially disagree because he believes what Pain said about the cycle of hatred. Naruto settles on a middle ground: he won't forgive Pain, but he won't kill him either (which ends up paying offvery well.
In the "Fire Temple" Filler arc, Sora tells Kazuma he won't forgive him if he insults his father again. However, Kazuma's response is "You won't forgive me? So what?!"
Naruto's fight with Gaara. Towards the end of the fight, he screams "I've HAD IT with you!" (in the anime) and head butts him. Later on, when both are too weak to even get up, he attempts to crawl ON HIS CHIN and defeat Gaara.
When Rukia is being arrested, she tells Ichigo that if he comes after her, she will never forgive him. After some complaining, however, she comes to terms with the idea of him helping her.
One of the earliest was when Orihime destroys the Numb Chandelier, after first declaring "I will never forgive those who hurt Tatsuki!"
After Captain Komamura yells this at Tousen and Aizen, he proceeds to immediately bring out his Bankai and asskicking ensues. His ass, that is.
Captain Hitsugaya utters this at Aizen a few scenes earlier, in response to Aizen stabbing Hinamori. Hitsugaya then gets worked.
Ishida utilizes it during an internal monologue as he's facing down Mayuri Kurotsuchi. It's implied at the time that he might one day end up eating his words as the internal monologue also indicates his Super Mode response to how unforgivable he views Mayuri's behaviour to be has not met the requirements he was giving for activating the power.
Mayuri had one of his own against Szayel Aporro Grantz. Szayel claimed to be perfect and Mayuri derided him for it, as a man of science would be rendered obsolete by perfection.
In the English dub of anime episode 144, one of these occurs when Ichigo, Chad and Uryu Ishida fight two Arrancar in Aizen's palace in Hueco Mundo. Ishida says that the less human Arrancar look, the less intelligent they are. One of the Arrancar does not take this well and tells Ishida so. In a subversion, Ishida proceeds to destroy him in the ensuing fight.
Says this multiple times after all his Fraccion have been killed. It is unclear if he is angry at the captains for killing them or if he is angry at the fraccion for making him get off his ass and participate in the fight.
Says it twice in a row after he survives the Vizard Hachigen trapping him inside a kido barrier and Captain Soifon blasting him with her bankai.
Similarly, Captain Yamamoto says this to the vice-captains when they need his help to destroy Allon.
He earlier tells Kyoraku and Ukitake that while he's willing to allow his other men to track down and kill Renji for saving Rukia from her execution, their dishonoring their position as captains is far more severe and forces him to deal with them personally. He also seems to take it personally that they were the ones to sabotage the execution, if his boasting about the pair is anything to go by; it's 'unforgivable' not just as his subordinates but as his favourite students.
Ichigo says it to Kumoi (who's holding Lurichiyo hostage) in anime episode 186.
After Tousen outlines his grievance against Kenpachi for killing the previous captain of Squad 11, Kenpachi asks if Tousen hates him, Tousen responds in the dub by saying that "(he) simply find(s him) UNFORGIVABLE!" (and says that Kenpachi is "beyond redemption" in the English version of the manga) before releasing his bankai.
Subverted in anime episode 198. During the fight between Espada #7 (Zommari Rureaux) and Captain Byakuya Kuchiki, Rureaux says it to Kuchiki after Kuchiki uses his bankai on him. Captiain Kuchiki then proceeds to effortlessly deflect Rureaux's special attack and destroy him with a single blow.
Anime episode 204. Princess Lurichiyo and her servitor Kenryu have a falling out over Kasumioji clan policies. To heal the rift between them, Ichigo and friends pretend that Kenryu is going to commit suicide in shame. Lurichiyo falls for it, but Kenryu blurts out the truth and Lurichiyo tells Ichigo and the others that what they did was unforgivable.
Anime episode 243. Yumichika says it to his zanpakuto's manifested spirit Ruri-iro Kujaku while fighting him.
Anime episode 289. Arrancar #0 Yammy Riyalgo says it to Captains Byakuya Kuchiki and Kenpachi Zaraki while he's fighting them. He then activates his Resurrección form.
Then there's that moment in the episode "Sweet and Sour Puss" when a monster called Togeira possesses him, taking away his ability to get angry and causing him to act kind and calm towards others even through all the beatings everyone gives him. Much later, after the King has been pounded and smacked around enough, Togeira, having been storing his anger from within him while everyone was beating on him, stores enough of his anger to unleash it all in one big mega-attack that has Dedede exploding into a massively firey rage that scares everyone and scream at the top of his lungs, "Now it's payback time!" Dedede eventually goes back to his normal self after he slips on a banana peel, therefore knocking Togeira right out of his own head.
In One Piece, Luffy angrily battles Zoro because he had slaughtered most of the villagers of an island (early on into the Baroque Works arc), who had given the Straw Hats plenty of food earlier on (pointed out by Luffy looking like an impossibly fat slob at the moment). Luffy was unaware that they were in fact bounty hunters. He even actually utters "Unforgivable" before the battle rages higher.
In fact, any time Luffy angrily shouts something about True Companions (at a villain, that is), it means this (as abusing one's True Companions or threatening his own is the one thing that will make Luffy go mad). After this, asskicking ensues.
Robin gets like this whenever someone destroys history in front of her (ruins, artifacts, etc.). In the Skypiea arc, the poor bastard who pressed her Berserk Button ended up begging for forgiveness. Robin's response? "No." * CRACK*
In the sixth movie, after Luffy thinks his entire crew has been eaten by a sentient plant controlled by a man with a palm tree on his head he shouts (repeatedly if I remember correctly) YURUSENAI! before proceeding to ... actually, get his butt handed to him for once.
Typically, dubs don't carry this phrase over, substituting it for something that sounds more Badass to the Western ear, but the Savers dub, Digimon Data Squad, actually uses this phrase frequently. And since Kurata is the biggest monster in the Digi-verse (yes, even Myotismon has met his match) everyone gets a chance to say it more than a few times. The dub of Digimon Tamers, on the other hand, used it once, by Takato and Guilmon as Gallantmon. It was Lampshaded by Beelzemon, who said "You can't forgive me? I don't recall ever asking for forgiveness!" And then the fight was on. It's not Narmful like the Data Squad version because Gallantmon didn't dramatically yell it, but stated it in a more matter-of-fact "this is why I must kill you" manner, befitting a literal Knight in Shining Armor.
Despite Digimon being a kids show, Gallantmon was willing to execute Beelzemon, and would have gone through with it were it not for the fact that said enemy's biggest victim, Juri/Jeri, asked for him to be spared.
In the third-to-last episode of Digimon Frontier, Lucemon, in his Chaos Mode, is having his Near Villain Victory moment of being about to finish off the DigiDestined with his Ultimate Sacrifice attack. Loweemon gets in the way and sacrifices himself against said attack, and Lucemon absorbs Koichi's data after the deliverance of both darkness spirits to Koji by him following that. Takuya does not take well to what Lucemon did to Koichi AT ALL. "How could you?! Lucemon, you've gone too far!!!!" Cue the appearance of Susanoomon afterwards.
Kouta, from Elfen Lied, is understandably miffed when he realizes that the young woman he's been helping since the first episode is the same one that he watched kill his father and sister years ago. And the Enfante Terrible Mariko considers her fellow lab project Nana having friends to be cause enough for this.
In the finale of G Gundam, Domon says this to Major Ulube, who has been behind all the crap Domon had to go through.
Domon: You piece of filth! My dad! My mom! My brother! Schwarz! My master! You've taken them all from me! And now Rain! Ulube... You'll pay for this. There's no way I'll ever forgive you!
Gundam SEED has Kira Yamato and Athrun Zala go through this with each other, appropriately named the Cycle of Hate, when they kill each other's respective friend in battle.
Gundam Age follows suit when Flit returns from his battle against Desil. As he's prepared to enter the battlefield one last time, he declares that he will never forgive the UE for killing Yurin.
This case was an excellent example of how much impact the phrase has lost over the years. When Flit says it, the viewers didn't give it much thought... and then were very surprised to see that, after the Time Skip, Flit meant what he'd said, and had dedicated his life to exterminating the UE, at any cost, regardless of how ruthless he had to be to do it.
Prime Minister: "Commander Asuno! If you do this, any hope of compromise will be lost! This war will continue until one side is completely wiped out!"
Flit Asuno: "Yes, I know. That was my intention from the beginning."
The fifth episode of Gundam 00 Season 2 has the A-Laws attacking the Cataron base (that contains war orphans as well as the members of Cataron itself), bombing the base, taking out all their mobile suits with ease and then letting loose little robotic shooting machines of death, the Automatons, as cleanup. When Lyle, secret member of Cataron that he is, sees the carnage, he goes Guns Akimbo on the robots and then turns on the A-Laws pilot above him, shouting "I'll never forgive you! I'll never forgive you, A-Laws!"
When Chrono and Rosette discover Aion's plan in Chrono Crusade (right after destroying much of New York City in the process of executing it), they fly into a rage and shout "Aion, we will never forgive you!"
Subverted in the Fruits Basket manga. Kyo thinks that Tohru's mother said this to him as she was dying after her fatal accident, and that she died hating him for not saving her. However, a flashback near the end of the series reveals that what she was trying to say was "If you don't pay your bill, I won't forgive you," an effort to remind him of the promise he made to look out for Tohru.
When Kagura almost lets slip to Tohru about Kyo's true form, Kyo covers her mouth and says "If you utter another word, I'll never forgive you!". In response, Kagura yanks Kyo's arm behind him and says "Oh you won't forgive me will you?!".
Priscilla from Claymore. She goes into a CRISIS of "Unforgivable", much like a Shinji's "must not run away", before actually going Berserk. The worst is that it was completely unjustified, and that her immature, self-righteous, ignorant attitude makes her do the heart-wrenching thing that is the basis for all the Claymore plot.
Her repetition of "Unforgivable" is more of a Madness Mantra, as it shows her absolute belief in the rules, and marks the beginning of her mental breakdown.
Clare from the same manga also utters this, which she mixes with "I will kill you" during her fight with Rigaldo.
Used to great effect in Death Note as Matsuda gives Light his much-deserved punishment.
To illustrate, Light uses a form of this to his girlfriend Misa at one point, when he's telling her not to screw up the task he's giving her.
In Azumanga Daioh, Tomo pulls off the "decayed" version of this on Yomi, whose "unforgivable" crime is... successfully using a vending machine after it ate Tomo's money and eating curry without spilling any. Leads to a Crowning Moment of Funny when Tomo chases Yomi around trying to whack her with a cafeteria tray, and hits Yukari instead.
In D.Gray-Man, someone once managed to get Allen angry enough to say this. EPIC asskicking ensued, but even so he was rather hopelessly outnumbered, and it took some timely assistance from the generals to take out all the mooks. Then things went downhill...
Also, occurs in episode 56 from Allen to Tyki.
In YuYu Hakusho seasonal Big Bad Sensui forces the heroes to play a video game made real by a pyschic child, who is playing as the game's Big Bad. As long as the heroes keep playing they can't die but if they win the game the kid dies, something Sensui conveniently forgot to tell his child follower. The team is reluctant to does this; but in the end one of them, Kurama, does the deed. Afterwards, Kurama doesn't utter this line but you can definitely tell he's thinking it; both by the expression on his face and his actions later on.
Possibly one of the more terrifying examples occurs in the manga adaptation of Breath of Fire IV. Right after seeing a village of child-summoners murdered, Ryu utters a "This Is Unforgivable" as he unleashes THE KAISER DRAGON (for those unfamiliar with Breath of Fire, think "nigh-unstoppable Kaiju-esque Dragon Of Mass Destruction"). It takes a Cool Down Hug from Nina (whom, for the first time in her life, is scared out of her wits by a dragon)—and this is after the Kaiser Dragon has not only decimated a LEGION but bored a hole through a mountain via its Breath Weapon.
Tatewaki Kunō says this ('Yurusen!' actually) in Ranma ½ during his first fight with Ranma, after he insults Akane. Cue ass-kicking - Kunō's.
Peach Girl: Momo says this when a trio of girls who are in love with Kairi destroy a necklace Toji gave her because they are jealous of her for getting Kairi's attention.
In Soul Eater, Death the Kid is as likely to use this in reference to anyone affecting his beloved symmetry as he is to any villain who likes to gather human souls for themselves and/or insult Shinigami-sama.
More dramatically, Spirit tells this to Medusa when she say she plans to abandon Crona.
Katekyo Hitman Reborn! Tsuna says this when he is enraged by Byakuran for triggering events that led to Uni's self-sacrifice, or self-imposed death. There is a good reason why that chapter was labled "The Last Blow."
Higurashi Kira Episode 2 had Satoko declaring that she would not forgive Tokyo Magika for hurting her Nii-nii. Later, Oyashiro Rika and Trap Satoko declared payback time before moving on to finish off Nail Ripper and send Takano flying.
In episode 5 of Gankutsuou Maximilien screams this during his fight with Albert.
Earlier, Battler was angered by Beatrice having gleefully laughed about Eva-Beatrice killing and reviving Rosa and Maria over and over again, so much so that he decided he wouldn't accept "that bitch" as his opponent. He told Virgilia that she could call her student if she wanted to, but that didn't mean he would forgive her. A disappointed Virgilia told Beato to try being more encouraging if she was to be forgiven by him and accepted as his opponent.
In the first season of Mermaid Melody Pichi Pichi Pitch, the heroines say this most of (if not all) the time to their enemies (be it the Dark Lovers or the Black Beauty Sisters) for whatever it is that they did that terrorized the seas or the people, be it making a theme park only to destroy it, chase down a boy who assaulted them with a water hose and retaliate by attacking, or even planning to force-feed chocolates to girls (which would turn the Mermaid Princesses to mermaid form).
In Shaman King, after Hao eats his brother Yoh's spirit (after which he attempts to digest it and therefore cause him to become one with him), Yoh's friends fly into a rage and make several futile attempts to attack him out of unforgiveness towards him. Even his fiance' Anna says that she will never forgive him. Things settle down a lot when Manta helps them defeat his Shikigamis, though, and more so when Yoh regains his spirit to the relief of all of his friends, and Anna welcomes him back.
Tao Len: ...You took my friend away and YOU'RE GOING TO PAY!!
The manga adaptions of the Zelda series done by Akira Himekawa seem to love this Trope. For example, in the The Legend of Zelda: A Link to the Past manga, after Agahnim sacrifices Zelda in front of Link and sends her to the Dark World imprisoned inside a crystal, Link shouts out, "Agahnim, I'll never forgive you!" before absorbing his magic with the Master Sword, leaving Agahnim shocked in a "This Cannot Be!" manner and sending the magic right back at him.
Also, in the The Legend of Zelda: Ocarina of Time manga, after Link is forced to kill his old friend, Volvagia, in order to free him from Ganondorf's control and awaken Darunia as the Sage of Fire, he calmly declares this trope to the Big Bad himself.
Darunia: I understand how you feel. Stay here and cool your head. If your emotions erupt you will never defeat Ganondorf. Link: You're right, Darunia. But I... I will never forgive Ganondorf.
In Fullmetal Alchemist, Winry finds out that Scar is responsible for the murder of her parents, she immediately picks up a nearby gun and points it towards him, only stopped by Edward. Later on, she runs into him and cooperates with him, but makes it clear that she does not forgive him for what's he done and only helping him because it is what her parents would have done.
Pictured above, Fujiwara no Mokou in the Touhou manga Inaba of the Moon and Inaba of the Earth likes using this trope when it comes to her bitter rival Kaguya. Face it, she just hates her so much because of the humiliation she gave her father.
Another villain example from Berserk: when Nosferatu Zodd's duel with Guts is interrupted, he roars this at the interlopers. This guy takes the Worthy OpponentBlood Knight dynamic really seriously.
An actual (anti) heroic example comes from Guts in volume 17, where he says something to the same effect. After getting a What the Hell, Hero? lecture handed to him, Guts rethinks how he dealt with avenging the Hawks after Griffith betrayed and sacrificed them during the Eclipse and that since he technically played a role in the group's downfall, he didn't have a right to avenge them... however, for what Griffith did to Casca during the Eclipse in which he viciously raped her in front of Guts and drove her insane as a result, Guts said that he would never forgive Griffith.
Even the otherwise lighthearted Tengen Toppa Gurren Lagann has an example: post-Time Skip, Yoko picks up teaching in an elementary school as job, hiding her real identity. When two rogue Ganmen show up and start wrecking the place, she gets angry. But when they threaten the life of one of her students (a little girl), she utters the line as she goes batshit fucking mad and breaks out the hidden armory. Asskickingensues.
In Episode 13 of G.I. Joe: Sigma 6, after having heavily damaged his ability to assume battle mode by blowing up his Power Stone in front of him, Duke battles it out with COBRA Commander in a one-on-one duel without weapons to have him prove how tough he is. After taking a few blows from the villain, he shouts out, "I've had it with you!" before fighting back and besting him with some more punches.
Duke:That was for the team...[punches and sends COBRA Commander sliding on his feet towards the edge] ...and THAT was for YOUR PAYBACK!
Izaya from Durarara!! mumbles this during a flashback of middle school. He's referring to Nakura who stabbed Shinra who is his only friend. Let's just say, Nakura was screwed the minute he stabbed Shinra by accident because of who his real target was. And 7-10 years later, Izaya extracts his revenge in the cruelest way possible.
In Mai Otome, while Arika fights Tomoe, she reveals that she was responsible for all of the things Miya took the heat and got expelled for. Arika only responds with shock until Tomoe, while mentioning her responsibility in the acid drop that injured Arika's friend Erstin, expresses pleasure regarding Erstin's death some time afterward, prompting Arika to respond with this phrase.
Tokyo Mew Mew does this really well, with the Mew Mews using this against the aliens and their Chimera at random times, either before or after transforming.
Ichigo/Zoey even uses this trope as quite a Badass Boast towards a monster attacking Tokyo in her dream in the beginning of an early episode.
Ichigo: You're a wicked monster and you've terrorized this city for the last time. Now you'll pay!
Rosario + Vampire: In chapter 41 of the second manga season Kurumu says "...won't forgive. I won't forgive you if you hurt Tsukune!"
Several members of Tsukune's Unwanted Harem threaten this at times, even to Moka when it looked like she might have been about to kill him.
In chapter 50 Tsukune says this to Miyabi because he invaded Mizore's village and planted a Forceful Kiss on her.
Although the intentions aren't carried over between meetings, this is often Hayate of Hayate the Combat Butler's manner when Nagi is threatened. Gilbert is frequently the target, and clearly frightened of the consequences of his actions, though not repentant not to try again at a later date.
Played for Laughs during an episode of Beelzebub. After a demon world plant eats the...thing he brought to life from a demon world book, Beel goes all fiery mad, and in his baby gibberish declares "I will never forgive you for this!"...and gets swatted aside. He is just a baby after all.
In Episode 9 of Sonic X: How dare you, Eggman! You destroyed Amy's lucky bracelet that she made for Sonic to protect him when he goes in the water, despite his fear of it. And she reacted with the line of "I don't believe it!" Not only did it make her cry a few seconds afterwards, but shortly after, she flew into a rage with fire burning in her pupils. You hit Amy's Berserk Button and you didn't even know it. Now she's REALLY PISSED at you, screaming at the top of her lungs, "Now you're gonna PAY!!!", which takes you by surprise. Once she charges at you and one of three of your current Robots Of The Week, Serpenter, shouting to you both "Don't mess with me!" along the way, and proceeds to kick its ass before going after you next, that's where you realize that you never should have made her this pissed off at you and that you're completely screwed. Cue Oh Crap.
Also, in the original edit, this is Sonic's final line at the end of the finale of Season 3, obviously declared against Eggman. It was replaced in the dub by another line in the form of "Life never stays slow for long! Thank goodness! Watch out, Eggman, I'm comin' at ya full speed!"
Hanaukyō Maid Tai La Verite episode 9. After Lemon, Marron, and Melon speak rudely to Captain Konoe Tsurugi, Konoe's lieutenant Yashima Sanae tells them "Speaking so rudely to captain...unforgivable!" She then chases them away.
A rather odd example occurs in To Aru Majutsu no Index when Touma says this to the villain of the current arc, Oriana Thompson, who is involved in a plot to brainwash the city. It's not the possibility of mass mind control that really upsets him, though, it's that her actions are interfering with the festival that's going on. Yeah, Touma can be a bit strange.
In Sukeban Deka, "Saki's" catchphrase is "Omaera, Yurusansezore!" (You Won't Be Forgiven!)
Every member of Fairy Tail will make sure that anyone who would disrespect their guild or hurt their friends will get no less than what they deserve.
Cowboy Bebop episode 22 "Cowboy Funk". During their confrontation on top of the ruined building Spike says "I will never forgive you" to Cowboy Andy, who's been interfering with his efforts to capture Teddy Bomber throughout the episode.
In Peter Pan No Bouken Hook says this to a giant sea creature (no, not the crocodile), which might make uninitiated anime fans watching the subbed version wonder why a giant sea creature cares whether Hook forgives it or not.
Black Cat: In the anime Train says this after Creed kills Saya.
FLCL. In episode "Brittle Bullet" Naota's father walks into Naota's room and catches him and Haruko accidentally kissing. He is interested in Haruko himself, so he tells Naota that he can't forgive him and challenges him to a duel for Haruko's affections.
Weed from Ginga Densetsu Weed says that he never forgives someone who abuses or kills other dogs just for the killer to save their own hides.
A lot of this flies back and forth when most of the cast of Bokura no Kiseki regains their Past Life Memories. To be specific, they are all the reincarnations of people in two groups: the original inhabitants of a castle in Zerestria that was invaded and destroyed by a country that was supposed to be its ally, and guests living in the castle who were from said invading country, Moswick. In particular, Meguro, the reincarnation of a squire of Zerestria, freaks out and tries to kill Nishina, who was a knight of Moswick. Teshimano and Harusumi talk him out of it.
Orin: What I ever do to you? Seymour: Nothing. It's what you did to [Audrey].
Alluded to in the film Gung Ho, when a shouting match between an American and his Japanese boss gets physical after the American says, "Oh yeah? Well, if you guys are so great, how come you lost the Big One?"
"Arthur Burns is a monster. An abomination. You were right to break company with him; what happened at the Hopkins place was unforgivable.
In the Chinese action film "Flash Point", the main character and detective Mah Jun, played by Donnie Yen, chases after a criminal on foot in the streets of Hong Kong. The criminal runs into a restaurant, grabs a young girl as hostage and holds her upside down by the legs. When Mah Jun catches up to him and holds him at gun point, the crook threatens to drop the girl on her head if Mah Jun doesn't drop his gun. Mah Jun complies but the criminal throws the girl forcefully aside anyway right outside the restaurant unto concrete ground injuring the girl. Mah Jun has a very brief Heroic BSOD and his face clearly shows a This Is Unforgivable expression followed by giving the attacking criminal a suplex from hell and then pummeling the man to to death.
Yes, even some Disney movies have these. In Mulan II, Mushu, pressured by Cri-Kee, admits to Mulan what he had done. Mulan is enlightened by Mushu's admittance, but also gets mad at him. She even says that what he did was unforgivable, and when he tries to ask to help some more, she replies with "You've helped enough."
In The Lion King, Simba says a line that comes close enough to this to Scar: "You don't deserve to live."
Some of the lyrics to The Lion King II: Simba's Pride song "One of Us" contain a variation of this.
Born in grief Raised in hate Helpless to defy his fate Let him run Let him live But do not forget what we cannot forgive
This was due to a misunderstanding - Kovu had been raised as a Tyke Bomb, but had already pulled a Heel-Face Turn by the time what he was convicted of occured; Simba misinterpreted the situation and refused to listen to otherwise, until the ending where his eyes were opened. The very theme of The Lion King II: Simba's Pride was Forgiveness.
In The Woman in Black, this seemed to be the Madness Mantra of the titular woman after her child went missing, as she believed he was being deliberatel;y kept from her. Unfortunately she died before anyone learned the truth, and her vengeful ghost got stuck in an infinite loop.
In Conan the Barbarian (1982), after Conan raids one of Thulsa Doom's towers and steals his treasures, he is most upset because Conan kills a giant snake guardian.
Thulsa Doom: You broke into my house, stole my property, murdered my servants, and my PETS! And that is what grieves me the most! You killed my snake. Thorgrim is beside himself with grief! He raised that snake from the time it was born.
Harrison: Your commanders have committed a crime I cannot forgive.
In the 2009 film Cracks the Diving Team reacts like this when the find out the teacher they trusted and admired molested a pupil and allowed her to die. The school seems to turn a blind eye until the whole team symbolically turns in their sashes
Michael, good Christian paladin type in The Dresden Files forgives and gives another chance to anyone and anything, even the odd Eldritch Abomination here and there. But, in the short story "The Warrior," when a Well-Intentioned Extremist priest kidnaps one of his daughters (knocking her unconscious in the process), ties her up in det-cord (explosive-stuffed rubber tubing) and rigs her with an electronic detonator — and then insists that a Walking Techbane wizard, whose very presence could have caused a malfunction in the detonator and set off the cord, be the one to release the girl — all bets are off.
Invoked and subverted in Shatterpoint:
Depa Billaba: You can't... you can't just forgive me. Mace Windu: As a member of the Council — you're right. I can't. As your Master, I won't. As your friend — as your friend, Depa, I can forgive everything. I already have.
In Dune, the depredations on the Zensunni people in the distant past are remembered in the oral tradition of their descendants, the Fremen, with the Badass Creed "Never to forgive, never to forget!"
In A Song of Ice and Fire, when Cersei beats the woman she thinks is Tyrion's mistress, Tyrion says "I have never liked you, Cersei, but you were my own sister, so I never did you harm. You've ended that. I will hurt you for this. I don't know how yet, but give me time. A day will come when you think yourself safe and happy, and suddenly your joy will turn to ashes in your mouth, and you'll know the debt is paid." He may not say the words, but this Badass Boast embodies the spirit of this trope very well.
Likewise, he doesn't say the words, but Tyrion's reaction to the lies and betrayal by his brother, his father and the aforementioned mistress is similar to this.
Though this comes back to bite Tyrion when Joffrey is poisoned on his wedding day; everyone assumes it was his fault, and he had nothing to do with it.
Actually quite a few characters react this way to being betrayed. Which happens quite a lot.
In the world of A Brother's Price, men are extremely rare and protected, so when some of the heroes find one who was killed, the ones who never knew their fathers are disgusted, but the ones who did have loving fathers are horrified, furious, even panic-stricken. Most didn't know the man in question, but this is the crime that really drives them to despise those responsible.
"What kind of animals could do this?"
Live Action TV
On Buffy the Vampire Slayer, Faith actually tries to get Willow to give her the whole "you can still be a good guy" speech, instead getting Willow telling her she's way past forgiveness. At least part of this is because she had kidnapped and tied up Willow though. Ironically, Willow becomes one of the few people who actually could later understand what Faith was going through, having gone evil and killed someone only to be brought back by someone showing caring and kindness when she didn't deserve it.
Still a Crowning Moment of Awesome for Willow, who is all alone in the mayor's office with Faith who has already gone rogue and is threatening Willow with a huge knife.
In season 8, after a Brainwashed and Crazy Angel kills Giles, Buffy refuses to forgive him. Buffy is also blamed for the world's magic being lost and even the other slayers tell her what she did was unforgivable.
The climax of anyToku show involves saying this phrase, followed immediately by a showdown with the Monster of the Week.
The Babylon 5 episode "No Surrender, No Retreat" opens with Captain Sheridan defiantly declaring "Enough is enough!", after President Clark's forces commit their worst atrocity yet, involving two Earthforce destroyers jumping out of hyperspace and, completely unprovoked, wiping out five commercial liners packed with 10,000 civilian refugees. And for the record, Sheridan is not even remotely kidding.
President Laura Roslin's speech in the following episode is arguably an even better example: "No. Not now. Not ever. Do you hear me? I will use every cannon, every bomb, every bullet, every weapon I have down to my own eyeteeth to end you. I swear it! I'M COMING FOR ALL OF YOU!"
This was deconstructed when Lee testified at Baltar's war crimes trial - Lee pointed out all the things members of the fleet had done that should have resulted in imprisonment (or execution) that had been "forgiven" by either Admiral Adama or the President, and that the only reason Baltar's crimes were unforgivable and deserved his execution was that no one liked him.
Lee: We have to break rules, we have to bend laws, we have to improvise! But not this time, no, not this time, not for Gaius Baltar.
An episode of Alias contains the following emotional speech. It doesn't lead to a physical fight (though these two characters do fight earlier in the episode) but it sets the tone for a temporarily broken relationship.
"What it comes down to is faith. What I was hoping you would say is, 'Sydney, I gave up, I gave up. I lost faith.' But what you came here for was closure. And there is not a chance you're getting that from me. I'm not gonna say 'I understand.' I'm not gonna sympathize with you and tell you how hard it must be for you... But you want to know how I am? I am horrible, Vaughn. I am ripped apart. And not because I lost you, but because... if it had been me... I would have waited. I would have found out the truth. I wouldn't have given up on you. And now I realize... what an absolute waste that would have been."
After things get out of hand at Degrassi during Vegas Night in the mid-season finale of "The Boiling Point", Principal Archibald Simpson has had enough of the crap he has had to deal with for his entire career at the school, and has this to say to the students: "By the time you all get back from break...you won't recognize this school at all." And he's not kidding — the next episodes see him instituting a school-wide discipline crackdown aimed at curbing the worst of the school's major problems.
Grizzaka: You've destroyed all of my warriors, my royal guards, and the great overlord Carnisoar. Finally, I shall destroy you! In fact, he doesn't. Shocking.
How I Met Your Mother had a version of this when Ted found out that Barney slept with Ted's ex-girlfriend Robin in a blatant violation of the Bro Code. Barney expects Ted to be angry but forgive him since Ted is very easy going and a bit of a pushover. Instead Ted is so furious at the betrayal that he punches Barney in the groin and wants nothing to do with Barney from that moment on.
A few episodes later, though, Ted forgives Barney.
In an episode of Merlin, Uther is blaming Morgana for her betrayal against the kingdom for trying to help the young druid Mordred escape. Morgana, who does not wish for Mordred to be executed, says that she will never forgive him if Mordred dies. Uther, on the other hand, states that he wasn't asking for forgiveness.
And when Merlin tries to prevent Mordred from escaping the Camelot Knights, Mordred kills them and warns him telepathically that he will never forgive him nor forget his betrayal towards him.
And again with Mordred in season 5 when Merlin reveals Mordred's plan to escape with Kara resulting in the latter's death.
In The Borgias, Rodrigo is telling his sons how to juggle the various bribes that will get him elected Pope. When one of them points out that his tactics are not exactly "holy", Rodrigo replies "God will forgive us, my son. But I will not. Forgive. Failure. From you, or your brother." Quite what he was threatening them with (if anything, since he does genuinely love his children,) is unknown, but since the line is spoken with all the verbal badassery Jeremy Irons can muster, it's understandably taken very seriously.
Stargate SG-1: After Teal'c shoots Sha're to save Daniel's life, Daniel refuses to believe that it was necessary and will barely acknowledge Teal'c's attempts at reconciliation.
TEAL'C: Is there not some form of human ritual in which I may ask your forgiveness?
DANIEL No. (walks away)
Interestingly, everything that happens after Teal'c kills Sha're turns out to be a dream of sorts. By the time Daniel finds himself back in the real world, he's already forgiven Teal'c.
In Once Upon a Time, Regina blames Snow White for the death of her lover and being forced into a crappy Arranged Marriage with Snow's father, the king (Never mind it was Regina's own mummy dearest who actually killed the lover - and the former Queen - and forced the marriage, Snow gets blamed). Snow White flees Regina's murder attempts and becomes a forest-dwelling bandit. Regina takes the throne and rules about as well as you'd expect. When Regina ends up in a peasant woman disguise and actually meets Snow again, Snow admits she pities Regina and would be willing to forgive her...until she discovers that her stepmother just executed an entire village down to the last man, woman and child for the mere "crime" of giving Snow a night's shelter.
This is Lenneth Valkyrie's big proclamation in Valkyrie Profile. She had been impassive up to now.
Vyers from Disgaea uses these exact words, twice, when Laharl, his would-be rival, unflatteringly refers to him as irrelevant and redubs him "Mid-Boss". He loses the ensuing battle, and the insulting moniker sticks with him for the rest of the game.
Kim Kaphwan from the Fatal Fury and the King of Fighters games has a variation of this. Whenever he fights a criminal (or simply evil, or perceived as evil) opponent, he points his finger at them and says "Aku wa yurusan!" ("Evil cannot be forgiven!"). Starting with the NESTS saga (King of Fighters 1999-2002), he even complements the pointing with Glowing Eyes of Doom.
His disciple May-Lee actually does something similar in King of Fighters 2001, Kamen Rider-ish pose and all.
Declared by Tails after Eggman appears to have killed Sonic in Sonic Adventure 2. He seems to largely forget about it when things settle down, though.
Used by Mickey in Kingdom Hearts II after Goofy has been (apparently) killed, triggering his costume change along the way and making room for what may be the most epic battle sequences in this game.
The original Suikoden lets you pull this at least twice with already-defeated foes. In one case, this is actually the wrong response, as the "villain" was actually Brainwashed and Crazy, and is one of the 108 Stars of Destiny. In the other case, it's perfectly fine to take this option, as the character is legitimately a self-serving sleazeball who caused the death of the lead character's best friend out of nothing more than petty greed — the conversation option for killing him actually reads "You're the one person I can't forgive."
Another moment is after Gremio, your protagonist's servant and protector, fools checkpoint guards into thinking that said protagonist is not the now-rebellious son of Teo McDohl, but his own son, and begins to shout at him for never doing anything right, even now being mistaken for a criminal. He is then stopped by pleading guards from killing his 'son' right in front of them. After safe passage, Gremio apologizes to the protagonist for his improvised actings, to which you can actually respond to with "Unforgivable!" This can go on for a short while, and messing with him is all fun and laughs until it nearly results in him killing himself out of shame. Yikes.
Subverted in Devil May Cry 4, wherein Credo utters this to Sanctus, who blatantly used Credo's sister as bait in his plans and thus the one thing that shook Credo's loyalty to the Order. The kicker? He said it after Sanctus fatally wounded him, and got his ass further kicked for his trouble.
In the Japanese version of Final Fantasy VI, after Cyan realizes that the Empire has poisoned Doma's water supply, he races around to find survivors, and when he races into his own room, he finds his wife and son dead. He screams at the Empire at the top of his lungs and races off to kill as many Imperial soldiers as he can, but not before muttering in shock.
Cyan: This is unpardonable...
Ruined by the otherwise okay Woolsey localization, which has Cyan yelling something like "THIS CAN'T BE HAPPENING! IMPOSSIBLE! IDIOTIC!"
Sephiroth: Fighting me won't help you recover the Crystals. WoL: I suppose. Sephiroth: Well then... Why come before me? WoL: You hurt my ally. Sephiroth: "I won't forgive you"... you might say?
Final Fantasy Tactics. Ramza, a purer than pure hero who only draws his sword once during a cutscene, who tries to talk every enemy he meets out of fighting, who is as forgiving as JESUS finally finds three people in all of Ivalice even he will not forgive: Algus Sadalfus, for shooting his adopted sister for no reason other than 'I'm a noble so I can do what I want'; Dycedarg Beoulve, his brother, for murdering their father, brother and trying to sacrifice their sister to an Eldritch Abomination; and Folmarv Tengille, for resurrecting the aformentioned murdered brother as a self-aware zombie, and making him fight Ramza.
Shouted by Sion Barzahd before one of the final battles in The Bouncer.
Sion: This is... This is unforgivable, Dauragon!
When Teen Gohan transforms into Super Saiyan 2 form in Dragon Ball Z Budokai 3, he screams "I won't forgive you!" If you don't know why, check Dragon Ball's entry under the Anime section above.
In Castlevania: Symphony of the Night, Alucard confronts a succubus who has been imitating his dead mother just to mess with his head, and conveys his intentions rather stoically before an inevitable boss fight:
Alucard: Demon. Death is too good for you.
He does say "Yurusan" in the Japanese, and is so VERY damn stone-cold about both that and the worse-than-death fate that his killing her in the dream-world will bring about (it's a death of the soul, so her spirit will never find rest and will wander lost for eternity). This followed by the only fade-to-black death in the game, and (in the original Japanese; the dub is uh...different) a very creepy cut-off scream from her.
And the sad thing is, you just know that he was a lot nicer than Dracula would have been if he found out about those shenanigans. 'Don't mention Lisa' is a good rule to follow.
Ishida Mitsunari from Sengoku Basara, whose vocabulary seems to be largely limited to screaming either this or the name of his rival Ieyasu at the top of his lungs. He even takes it one step further by refusing to forgive not only Ieyasu, but the whole world. Even selecting him from the Character Select screen has him uttering "I will never forgive you".
In the Ace Attorney series, there are two things Phoenix Wright considers completely "inexcusable", as he says in case 3-3: Poisoning, and betrayal. There's a deep, personal reason for this.
Used for humor in the first case of Ace Attorney Investigations. A body is found in Edgeworth's office, what gets him really mad? Someone broke his prized tea set!
Edgeworth: ...Nnngh... That killer is going to pay! This tea set...! Gumshoe: Yikes! You're really mad over this! Edgeworth: This tea set is very dear to my heart and can only be bought in England. It cost more than your whole month's paycheck. Gumshoe: W...Whaaaaaaaat!? Now I feel like the killer's wasted one of my monthly paychecks!
Shelly de Killer. After finding out that his client taped the crime scene for blackmail, he breaks his contract with Engarde, returns Maya to Phoenix and swears that Engarde will get his just desserts. The moral of the story: Don't piss off an assassin.
Edgeworth: Some time in the near future, one very betrayed assassin may appear before you. Needless to say, that man is very good at what he does. I'm sure you know what I mean, if you watch this video.
Phoenix also views Franziska's suppressing a photograph during Maya's trial this way. It turns out there's more to this tactic than he thinks, but she is still trying to get Maya convicted by any means necessary.
Phoenix: (Unforgivable, Von Karma. Suppressing evidence like this... You're as bad as your father!)
Surprisingly often used in Fire Emblem. For example, Renault versus Nergal in FE7: "You villain... You cursed him! Your crime can never be forgiven! I will end you with my hands. In the name of my lost friend!" Or Jill versus Ashnard in FE9: "...Ashnard... Ashnard!! ASHNARD!! I...will never forgive you! NEVER!!!" Or Elincia versus Ashnard: "Yet my purpose here is to defeat you. In the name of my father, my mother, my lord uncle, and the countless citizens of Crimea... You murdered them all! And I will never forgive you that!" Yep, FE loves this declaration.
In the seventh game, adorable assassin-in-training Nino is given the chance to confront Sonia, the woman who murdered her parents and adopted her with the intention of raising her as a Tyke Bomb. This failed, so Sonia tries to have her killed. THAT fails, and Nino eventually joins the heroes. During their confrontation, Sonia gleefully admits to slaughtering Nino's parents. Nino doesn't take it well. "Aaahhh!!! You're no perfect being! You're a monster in human form! No mercy! No forgiveness!!!"
Lyn in FE7 has two of these. The first is against her granduncle, Lord Lundgren, for trying to assasinate her, poisoning her grandfather (his own brother), and harming the people under his charge to whom he has a duty. The second is an actual utterance, when she, Eliwood and Hector discover the murder of Leila, an Ostian spy and Matthew's lover:
Lyn: Unforgivable! This is... a foul deed. Beyond foul.
In his own story path, Hector shares in the above (for Lyn's second This Is Unforgivable) by swearing a vendetta against the Black Fang until he finds the one responsible. He also echoes Lyn's "I have neither pity nor mercy for you" when he confronts Nergal. Notably, Eliwood does not possess this quality
When X declares to Gate in Mega Man X 6, "Time to teach you a lesson, Gate! You used Zero's DNA to cause the Reploids pain. All for your own ego! I won't forgive you!"
Also, for a villain example in said franchise:
X: So you're the Big Cheese? Ride Boarski: Big Cheese?! Arggghhhhmm! How dare you call me that! I'm the Head Honcho, for crying out loud! X: OK, whatever you say. I order you to disband this motorcycle gang! Ride Boarski: Motorcycle gang?! Why you!! You've gone too far! I'll make you pay for this, with a duel!
Maverick Hunter X, the remake of the first game, features this from X towards Sigma before their final battle. "What you've done is unforgivable, Sigma!" At the time, Zero had just died, and X is completely fucking furious, and it's reflected in the dub delivery, which actually gives the line weight.
Rosenkreuzstilette also enjoys using this trope as well. For example, after laying her undead grandfather Raimund Seyfarth back to rest in her alternate mode, Grolla, both infuriated and deeply hurt, declares this trope in vowing to punish Graf Michael Sepperin for disrupting his peaceful slumber. This is not the only "This Is Unforgivable" moment in the game.
Grolla: Michael Zeppelin... your reasons mean nothing to me. There will be no mercy. You shall pay for this with your life.
Also, in the main game, Spiritia and Lilli say two variations of this trope to Iris in Iris Stage 3. First, Lilli shouts out "You're gonna pay!" to her, and Tia follows with the common variation of "Iris, I'll never forgive you!"
Zorne is also quite fond of using this trope, especially as one of her pre-battle quotes or when Grolla confronts her after having defeated her friend Trauare, which is one of quite a few things that can press Zorne's Berserk Button.
Zorne: About time you showed up, Grolla! If it weren't for you, Trau would still be a part of RKS! You're gonna pay for that!
Guilty Gear uses some "This Is Unforgivable" moments as well. For example, May says this to I-No when she catches her tormenting and hurting her friend Dizzy.
BlazBlue is another game that also likes this trope. For example, Ragna the Bloodedge, the main protagonist, says this when he uses Hell's Fang on his hated rival Jin Kisaragi. The same thing is also done in his winquote against him.
Ragna: I'll never forgive you, you son of a bitch. I was gonna tell you to die a slow, painful death, but I don't got the patience to wait around, so you're dying now.
Also, in Continuum Shift, Kokonoe declares this to Hazama when he fights Lambda-11 in his arcade mode run.
Kokonoe: I've just got one question to ask you. Why did you betray my mother? Hazama: "Betray?" Come on, don't give me that. It's not like the Six Heroes were buddies... then the other day, I told the old man, "We're buddies, right?!" Hahahaha! Kokonoe: You... you bastard! I'll never forgive you! Lambda! Kick the shit out of him!
And for the encore there's this exchange between Ragna and Hazama/Yuuki Terumi in Continuum Shift's True Ending:
Ragna: Terumi... Terumi... I will never forgive you! Hazama: You won't forgive me? Like I give a damn! Just shut up and die already!
Since Hazama/Yuuki Terumi is sustained by hatred, never forgiving him is playing him straight into his hands... Which really is a bloody shame, because he is good at crossing the Moral Event Horizon and then pushing waaay past it, to infinity and beyond. For the Evulz.
Reimu Hakurei of Touhou uses these words when Sanae Kochiya fights her in her story run in Touhou Hisoutensoku because she accuses her of making a huge pitfall trap for her to fall into:
Reimu: Talk is cheap! Making such a huge pitfall trap is unforgivable!
As does Ninja Maid Sakuya Izayoi in Koumajou Densetsu II during the final battles upon learning that Yukari was behind everything that happened with her mistress:
Yukari: Ah, I wonder if the air was too heavy for a vampire. Sakuya: Yakumo Yukari... you!* Just in case we're not fully aware of how pissed Sakuya is, the particular form of "you" she uses here is kisama. Yukari: Hahaha...don't let yourself boil over yet. There's more to come. Sakuya: I can't...I'll never forgive you for this!* The Japanese Sakuya uses here is "Omae wa zettai ni yurusanai!" which translates to "I will absolutely not forgive you!" In other words, Yukari is in for one hell of an asskicking.
In AdventureQuest Worlds, the hero helps the Great Godfather of Soul send a Royal Jar of Honey to Lord Ovthedance as a peace-offering in order to help him get the magical shoes the Horc used to cheat him out of victory in dance contests. What the hero doesn't know is that the Godfather was setting up Lord Ovthedance by claiming he cheats in dance contests. After beating him and realizing that his shoes aren't enchanted (the Lord didn't need enchanted shoes to win anyway), the hero realizes that the Godfather lied and used him/her, apologizes to the Lord for seeing to it that he's in no shape to dance at that point, and decides to show the Godfather who's boss. After receiving dancing lessons from Lord Ovthedance, he/she challenges the Godfather to a /Dance-Off competition, and wins the /Dance /Dance Minigame, taking the title of Dancing Champion. The Godfather isn't too happy about that, and that's when, while he declares this trope to the hero, Chaos Lord Discordia is mentioned for the first time ever by him.
Great Godfather of Soul: Have you come back to rub your victory in my face, hero? Someday, with Chaos Lord Discordia's help, I'll make you pay for taking my title from me! You can count on that!
In the Golden Ruins area of the Frostval events, the hero and Blizzy confront Maximilian Lionfang, who has kidnapped the Spirit of Frostval and stolen the presents from the town of Frostvale. Believing that the world must suffer for bending its will to evil and that there can be no peace until all evil is completely and permanently vanquished, Lionfang burns the presents with his whip as a demonstration of one of the "prices that Lore must pay for the pathetic truce between Good and Evil." A horrified Blizzy lets out a Big "NO!", Lionfang gives off an Evil Laugh, and the hero doesn't take that too well. He/she shouts to him, "You'll pay for that!" before proceeding to hand his butt to him on a plate for the second time and afterwards tell him, "Keep the change, you filthy animal," which is also a memorable line from Home Alone.
In the 2011 Friday the 13th event:
One-Armed Bandit: My gang is all over this area. You'll never make it to that ship! [to Voltaire] You with the guitar... This is all YOUR fault. I'll get you for this!
He said that to Voltaire because he blamed him for his involvement in the hero defeating him, and wanted revenge on him for it. He would later keep true to his desire for revenge against him by ambushing him during their confrontation with Lord Krom Wrath, and dragged him somewhere where they could settle their score while Deady in his One-Winged Angel form of Urkor Malravenus fought Krom Wrath and the hero used the Vorutanian Key Blade to beat Yahorneth, save the world from being taken over by the Necrus and Krom Wrath, and force the Necrus to retreat back to Necronus. It later turned out that Voltaire survived his fight with the One-Armed Bandit and in the process of doing so got his mechanical claw in place of one of his hands.
In Doomwood Part 2, Gravelyn calls out Noxus for betraying her and having Chaos Vordred take her hostage.
In the Bloodtusk saga, after sending the Horcs and Trolls back home to rest up from all the fighting they did after defeating the alliance soldiers led by Cynari and Tibias, the hero makes a declaration that, when he/she finds the Chaos Lord running the madness taking place in Bloodtusk Ravine, he/she will make them pay, especially for murdering Antiphuus. He/she also gets an idea on where to start looking for information on the Chaos Lord. The Chaos Lord later indeed turns out to be Krellenos.
Hero: DRAKATH! I know you have a hand in this. When I find your new minion, I will make them PAY! And I need to know who! ...I'm not sure where to start, but I think I have an idea.
Later, in the same saga, Khasaanda has become enraged at Krellenos for abandoning her, ruining everything about the ravine and having chaorrupted and caused the death of their own brother. So what does she do? She usurps his Chaos powers and then kills him using a telekinetically-driven weapon from a chaorrupted Alliance soldier. After that, she plans to use her new Chaos powers to exact revenge on Drakath for the chaorruption and deaths of her brothers.
The finale of the Swordhaven saga has the Hero declaring his/her intent to make Drakath himself pay for driving King Alteon to madness through his chaorruption, causing the death of Princess Brittany at the hand of her own father, and the horrible devastation wrought upon Swordhaven by the Chaos Dragon.
In the seventh dungeon of Paper Mario, the Crystal Palace, one of the puzzles to solve involves Bombette and five Duplighosts disguised as her. This puzzle is quite simple to solve, really - all Mario has to do is hammer all five of the Duplighosts disguised as her. As a matter of fact, Mario can tell who the real Bombette is because she's the one who says that she will never forgive him if he messes up.
In One Piece Unlimited Adventure, when Robin says before the fight with Eneru that she'd rather not see him again (in canon, he nearly killed her and almost destroyed Sky Island), an audio clip of her saying "Unforgivable!" is heard. When Shanks uses his ultimate attack, he yells "I won't forgive those who hurt their friends!" (a mistake in pronouns, as it's a reference to his being willing to tolerate insults, but not those who threaten his friends)
In Deus Ex, after you escape from UNATCO, Gunther says in a voice full of hate "No, I cannot forgive. No... not the killing of Agent Navarre. I will follow you. Denton; I will get you!
In Mass Effect 2, Paragon Shepard can state this during a conversation with Mordin, where he reveals that he redistributed a modified form of the genophage to the Krogan, since they were adapting to the previous strain of the Virus. While Mordin rationalises it that it was simply to keep the Krogan numbers in check so they could not threaten the Galaxy again, Shepard gets pissed, calling it practically a War Crime that the Salarians don't have the courage to admit responsibility for.
Paragon Shepard also has this attitude when discovering the true purpose of Project Overlord, where the Paragon Interrupt is pistol-whipping Dr. Gavin Archer for experimenting on his brother and hooking his mind into a machine. When Shepard re-encounters him in 3, it's clear they still have nothing but utter contempt for him, even if they are currently saving his life again.
Paragon Shepard can invoke this in 3 to try to end the Geth and Quarian conflict, stating that the Geth don't want to fight the Quarians and that throughout their history, all they've done is act in self-defence due to the Quarians being the aggressors in the conflict. With a high enough Paragon rating, Shepard can even end the entire war by brow-beating the Quarians into a cease-fire.
Persona 4's Yosuke Hanamura yells this at Adachi Tohru, who has just taunted him and the rest of the Investigation Team with the fact that he was the one responsible for the murder of both Mayumi Yamano and Yosuke's beloved senpai Saki Konishi, as well as manipulating Namatame into carrying out his evil work, all for his own twisted amusement.
In The Elder Scrolls V: Skyrim, in one of the late Thieves' Guild quests, you enter a dungeon to find an entire group of bandits slaughtered. When you meet up with your friends, they explain that it was the work of the traitor you're hunting down. Brynjolf says this:
Brynjolf: Crime is one thing. Murder is another. Mercer will pay for this.
Batman:You stopped being my son when you killed Dick Grayson. He was my son.
After the fight his victory line is:
Batman: You're dead to me.
Star Wars: The Old Republic: The Consular's eventual Padawan, Nadia Grell, is the Spoiled Sweet daughter of a senator, and one of the nicest people you will ever encounter in the game. Daddy Grell turns out to be a fine statesman and stalwart ally of the Consular until the Sith kidnap him. When Consular and Nadia charge in as Big Damn Heroes to save Daddy Grell, it's too late - the Sith tortured him to death. Sweet little Padawan Nadia loses it, and even if you try to intervene, that Sith is dead by her hands.
In the first video (and most popular) of the Unforgivable series, this trope is averted really, really hard. The narrator essentially meets a woman while he is plotting to buy pants with stolen money, gets her number, and takes her out on a date. This date consists of her buying him food, him treating her rudely, and eventually him forcing her to satisfy his libido in the bathroom of the arcade to make up for the fact that she had two siblings. He then shouts, "UNFORGIVABLE!" at the end. However, after watching the rest of the video, this only proves that he is an extremely angry person who gets upset about minor things.
In Tasakeru, Zero says this after N'Ktane pulls an incredibly cruel sneak attack in Book IV. As he's a former Samurai, the usage is deliberate.
In Dungeon Keeper Ami, what amounts to this happens during the invasion of Dreadfog Island, when Empress Mercury learns that the undead priests of the Crowned Death have plucked out the eyes of eight thousand captive innocents they intend to sacrifice — including children — so that they couldn't cause trouble. Ami's response?
Cold rage simmered in Ami's heart as her bright crimson gaze focused on the fog-covered island, a dark stain against the setting sun. Crowned Death and his minons would pay, she promised herself. Her armoured gauntlets, balled tightly into fists, groaned as her fleet charged onwards into the blood-red sunset. They. Would. Pay.
In season 1 of Winx Club, when Bloom is taking her simulator test, her rabbit Kiko secretely joins her. When the Trix sabotage the test to see if Bloom has the Dragon Flame, they try to get her angry. They eventually manage to get this reaction out of her when they shoot Kiko into lava. Bloom goes crazy and easily drives the Trix away, but the Trix do confirm that she has the Dragon Flame. Bloom and Kiko turned out okay, since it was mostly just a simulation.
In Teenage Mutant Ninja Turtles (2003), Raph gets so angry over having been paralyzed by one of the hornets earlier in the "April's Artifact" episode that he declares, "Bugs... must... PAY!"
Later, in "Same as It Never Was", Donny becomes enraged at Future Shredder after the Karai Legions kill Future Mikey to such horror from Don that he lets out a Big "NO!", plowing his way through the androids declaring that Future Shredder will pay for it, just before blasting away at Future Shredder with his exo-suit.
Also, in the same episode, after Future Karai kills Future Leo from the back, an enraged Future Raph, after letting out another Big "NO!", clearly tries to kill Future Karai for it. He gets killed by her... only for Future April to avenge them both by blasting Future Karai hard enough to kill her.
The title character of Dan Vs. does this in every episode. Once he wants revenge on someone (or something), almost nothing will convince him to do otherwise.