Azula becomes progressively more unhinged (see pictures) throughout the Grand Finale, kicked off by the betrayal of Mai and Ty Lee. She really starts going nuts when her father Ozai promotes her to Fire Lord, only to name himself the Phoenix King, effectively rendering her a Puppet Queen, goes even farther when she fires her servants out of paranoia when she thinks they are plotting against her and she hallucinates a conversation with her mother, and climaxes after Zuko and Katara interrupt her coronation and defeat her in an Agni Kai. Her last scene is of her weeping, screaming, and writhing on the ground; chained, and pathetic. Zuko can only look on in pity, while Katara can't even bear to watch. Word Of God has stated that she's now in a hospital and is supervised around the clock (not that it makes the breakdown any less disturbing to watch).
Ozai himself undergoes this. At the start of his battle with Aang, he's smug and confident. But after Aang finally achieves the Avatar State and proceeds to kick his ass all over the place, Ozai is visibly terrified and tries to FLEE. After Aang strips him of his powers, Ozai is simply a wretched shell who speaks in a monotone, "don't give a shit about life anymore" voice.
Amon/Noatak has one after his fraud of actually being a waterbender is revealed to his Equalist followers. He flees with his brother (who like him is a Tykebomb to their vengeful former crime boss father) and "start anew". He's seen smiling, but it seems on some level he knew it would never work, because a single tear comes from his eye before his more despondent brother commits a Murder-Suicide on them.
Zaheer's might have started when P'li is killed; though it more immediately makes him "let go his earthly tether" and gain the mythical Airbender power of true flight, it made him very cold and detached. His plan to poison Korra to invoke the Avatar State while she dies (which would permanently end the Avatar cycle) goes as onemight expect. Korra, gooned on all the power of the Avatar State as it attempts to resist the lethal poison, clearly has Zaheer's murder on her mind, and he can do nothing but flee her terrible wrath. Though he eventually gets the upper hand as the poison wears Korra down, he is then assailed by all the new Airbenders. His efforts to escape their tornado fail, and he's Laughing Mad and angrily delusional after being thwarted in his attempt to kill Korra... and then Bolin literally "puts a sock in it".
Kuvira's starts after she chose her Empire's expansion over Bataar being exploited as a hostage. With Bataar's disillusionment, she lost all her inner circle. Once the Hummingbird mecha-suits and Korra's massive ice wave pose a credible threat to her Colossus, she starts to lose it. As Korra and her comrades tear apart the Colossus from the inside, her desperation pushes her to tear off whole parts of the Colossus in attempts to stop them. And after the Colossus is effectively destroyed, her stubborn refusal to surrender despite not even being physically fit to fight leads her to flee... right into the spot in the Spirit Wilds where the Spirit Ray Cannon landed, leading her to rashly fire it off in a last ditch attempt to kill Korra... which leads to a Phlebotinum Overload, from which Kuvira is spared death from only because Korra reaches a new pinnacle of power in deflecting the beam in an effort to save her. Hers has a more graceful ending after Korra gives her a Not So Different lecture and she has a Heel Realization.
President Lex Luthor suffers from one of these at the beginning of the Justice Lords arc in Justice League. As the alternate-dimension League close in on him, he's cryptically mumbling "They couldn't see the beauty! No imagination! It could have been so perfect!" We never learn exactly what Luthor was up to prior to this, but the way normally cool-headed Lex seems to be coming apart indicates it was an outcome he obviously didn't plan for. Also, he's killed The Flash. When Superman finally confronts him, Lex actually threatens to start a nuclear war if Supes doesn't back down.
Superman: I let it get this far because of the law and the will of the people. Lex: The people? This is all their fault! And they're going to burn for it... BUUUUURN!!!
Aku, the evil shapeshifting demon/wizard, does this in episode 13 of Samurai Jack in which he tries to convince the children of the world that Jack is the true villain and Aku is actually a hero. He does this through telling modified fairy tales where Jack is the bad guy. After being interrupted and contradicted a bunch of times during the fairytales by some terrified witless children, he starts to completely mix up fairy tales in increasingly hysterical, convoluted (and incredibly hilarious) ways. Finally, it ends with him shouting "THE END!" and swirling away.
When the Master Planner's (alias Doctor Octopus) master plan falls apart, and he is briefly overwhelmed by information to boot, his reaction is relatively subtle. Rather than visibly lose his composure, his voice becomes frighteningly quiet and deranged (if his eyes were visible, they would probably be bulging) as he does everything in his power to sentence Spider-Man to his doom.
Venom completely loses it when Spider-Man uses the scalding water in the school to forcibly remove his symbiote. He collapses into a mess crying over losing it and yelling mad phrases. Spider-Man is suitably disturbed.
Riddler gets one after Batman escapes from what was supposed to be his last Death Trap, then tricks Riddler into revealing what he did without upholding his end of the deal of telling Riddler how he managed to escape, in essence ruining Riddler's already failed attempt at reform. The episode ends with him screaming wildly in his cell in Arkham:
"It's impossible, I tell you! Impossible! My trap was perfect! How did he do it? I must know! SOMEBODY TELL ME! IT'S NOT FAIR! THERE WAS NO WAY, I TELL YOU, NO WAY HE COULD HAVE GOTTEN OUT! SOMEBODY TELL ME! DO YOU HEAR ME?! SOMEBODY TELL ME HOW HE DID IT! I HAVE TO KNOW! I HAVE TO KNOOOOOOOOWWWWWWW!"
I HAVE TO HAVE IT! I HAVE TO! AAAAAAARRRRRGH! AAAAAAAAAH!
Two-Face's split personality disorder eventually forces him to assume a 3rd personality as a vigilante who wishes to rid Gotham of all the corruption caused by his own alter ego. Eventually the two personalities forget they're one and the same and Two-Face, after being arrested, could be heard putting himself on trial in Arkham.
Baby Doll (in the episode of the same name) leads Batman into a carnival funhouse. Once he's cornered her in its hall of mirrors, she is understandably startled and then bittersweetly distracted: the mirrors are the Hand Wave that allow us to see how Baby would have appeared if her growth hadn't been stunted. Watch the rest of the finale here.
Batman: Mask of the Phantasm: The ending with the Joker laughing manically while in the clutches of the Phantasm as they slowly smoke-teleport away while everything burns around them.
In "Soul of Silicon", a robotic Batman flips out when he realizes he just "murdered" Batman, destroying the Batcomputer before H.A.R.D.A.C. could be resurrected.
Look Charlie, You had a busy day. All this running around, all this excitement with... BATMAAAAAAAN!"... "NOOOOOO...."... "BATMAAAAAAAN, BATMAAAAAAAAAAAAN".
The Ventriloquist gets one at the end of his first episode as well. You'd think that Batman "killing" Scarface and freeing the poor, downtrodden puppeteer would give him some relief, but seeing Scarface dead reduces the Ventriloquist to a screaming, sobbing wreck. He's better the next time we see him.... Presumably because he's carving a new dummy.
Derek Powers has one spanning season 1 of Batman Beyond after he's turned into Blight... culminating in an enraged psychotic break that brings whole new meaning to "having a meltdown".
At the end of the episode "Joyride", after Scab's hijacked ship crashes, the episode ends with him trying to make it fly again, then pounding on the controls, gnashing his teeth, and generally losing it. (It didn't stick — in a later episode, he's back on the streets.)
In the season 2 finale, Vlad's most desperate plan to obtain Danny as his son has him building a perfect clone of him with plans to kill the original one after. As if that wasn't crazy in itself, everything was going great until Danny's Opposite-Sex Clone does a Heel–Face Turn (because Vlad threw off a Rant-Inducing Slight) and teams up with the hero to destroy the clone lab, including the perfect clone. Vlad, once calm and preserved, goes insane, delivers a very emotional Big "NO!", and was downright close to murdering everyone if not for a timely rescue by Danny's friends. And it's permanent. Oh so painfully permanent. In season 3 it's shown that Vlad's attitude towards Danny has drastically changed. Vlad used to think that of Danny as a son who needed to be convinced into joining him. After that breakdown, Danny became an all-out enemy, and Vlad wanted nothing more than to destroy him and see him suffer.
In his second appearance in the series' third tv movie, the evil ringmaster Freakshow suffered from one when Danny played on his jealousy of ghosts, resulting in him using the powerful RealityGauntlet to become a ghost himself, which is exactly what Danny wanted so he could use the Fenton Thermos to trap him and save the world.
When Ember'sPopularity Power stopped working and her 'fans' stopped screaming for her she freaks out. She tries to get them to chant her name but no one does. Ember then falls to the floor in a twitching mess, which is how Danny captures her.
Henry Peter Gyrich was always a little unhinged, but after years of being on the losing end of an on-and-off conflict with Professor Xavier, topped off by weeks of (offscreen) struggling with him to ratify the latest anti-mutant bill, he finally cracks in the last episode. This turns out to be the "dangerous" version, as in the space of a minute, he throws his whole reputation out the window to make things go very, very bad.
This was deliberately induced in Graydon Creed. Throughout season 2, he's a Smug Snake bigot, leader of KKK expy "The Friends of Humanity" and displays no emotions beside contempt... until Wolverine shows up and recognizes Creed as the son of Sabretooth. Confronted by an image of his abusive father, Graydon falls to his knees, screaming and weeping about how he's "not like him" and how he's "normal" before grabbing a gun and shooting the hologram, even though he knows it isn't real, howling that it isn't his father. Let's not even think about what Creed endured with Sabretooth as his dad, to provoke such a strong reaction. In his last appearance in the series, he's lost it, and his fellow FoH members are tired of his failures. They offer him one last chance to redeem himself by ordering him to kill his mother Mystique and his brother Nightcrawler. When he messes that up, they punish him by leaving him at Sabretooth's doorstep. The last that is heard of Graydon Creed in the series is his pitiful whimpering as his father grabs him and says "Come to papa..."
Megatron: Lugnut! This field test has been a complete failure! Order the clones back to the moon! Lugnut: I am sorry, master. The clones' flight capabilities have been disabled— Megatron: Then destroy the Autobots! Destroy the city! DESTROY ANYTHING THAT'S NOT ME!!!
The Megatron of Transformers Armada has the "catatonia" kind of breakdown after Optimus Prime's death. Without a Worthy Opponent to challenge him, he's so despondent that he can hardly be bothered to do anything anymore.
The newest Megatron of Transformers Prime is probably more terrifiying than his Animated conterpart. Taking charismatic and replacing it with... sadistic. He finally has a breakdown of his own after Optimus Prime destroys his new base, beating him badly in the process.
In the miniseries G.I. Joe: Resolute, Cobra Commander is a little... "off" to start with, but by the end of the series, he hacks a roomful of his own men apart and paints a cobra symbol on the wall in blood because one guy had the nerve to tell him that the death ray was not fully charged at the time.
In "Scooby-Doo! Mystery Incorporated" Professor Pericles goes through one following the episode "Wrath of the Krampus" which he shown to be more prone to psychotic outbursts and is willing to kill anyone in his way.
The guy-with-no-life Jenkins in "Make Love, Not Warcraft" does the "shutting down" version when his character is finally killed in World of Warcraft. We don't get to see what he does after those first few seconds, as he's only ever shown in-game and in brief flashes sitting in front of his computer, almost reacting to what happens there. Being defeated makes him... flinch.
When Cartman learns that he murdered his own father he simply stares in empty shock and doesn't even resist when Scott rams his head into a chili bowl. Cartman being Cartman, the cause of his BSOD is the discovery that he's actually part ginger.
In "Cartmanland", Cartman starts going downhill when he has to keep letting more and more people into the park he bought with his inheritance money in order to hire the people he needs to keep it going, eventually just selling it back to the original owner. Then, officials take the money he made due to tax evasion and a lawsuit from when Kenny died earlier on, and it's revealed that he owes several thousand dollars more and the original owner refuses to sell the park back to him, leading him to break down in tears and a litany of swearing. Also, in "HUMANCENTiPAD", when Cartman didn't get his way, he blamed God, who struck him with a bolt of lightning. Cartman ended up in the hospital, bandaged and crying.
In "Christian Rock Hard", Cartman learns that Christian record companies use different certifications for their sales, meaning that Cartman technically hasn't won his bet with Kyle by making a platinum-selling album. Cartman flies into a rage, smashes his band's myrrh album and screams blasphemous obscenities in front of a horrified crowd of Christian rock fans.
Butters AKA Professor Chaos has this in "The Simpsons Already Did It" where, after watching every Simpsons episode to make sure one of his plans won't be a ripoff of an episode and leaving to inact it, he hears a commercial of Bart doing the same thing. He then hallucinates of every place and person looking all like Simpsons characters. He gets better when he learns that the ideas the Simpsons used were used before the Simpsons too.
In "Cash for Gold", Stan calls the host of a shopping network that rips off elderly people and tells him to kill himself. At the end of the episode, it is revealed that since Stan called and told him to do it, elderly people are calling him constantly, repeating Stan's request until he snaps and finally shoots himself.
Exo Squad's Big Bad Phaeton loses it after he contracts automutation syndrome in the aftermath of a battle with J.T. Marsh. He becomes more enamored with doomsday weapon projects, abandons all subtlety, and resorts to grandiose speeches and rants as everything falls apart for the Commonwealth due to his increasingly irrational command decisions. One of the more justified examples since the automutation syndrome is gradually liquefying him. That can't be good for one's sanity.
At the start of The Venture Bros. season 4, Phantom Limb shows up utterly batshit crazy, with a "Revenge Society" consisting of a toaster, a coffee mug, and a black patent leather Ferragamo pump.
To top it all off the pump belonged to his ex, Dr. Girlfriend, who was by then Dr. Mrs. The Monarch.
He gets better after Professor Impossible's Face–Heel Turn and the restoration of his missing limbs, returning to his season 2 personality and style. He then starts staffing the Revenge Society with actual supervillains (and some D-list would-be fillers).
On My Life as a Teenage Robot, Vexus falls from power in The Movie. The next time she's seen, she's gone insane, planning to blow up the asteroid she's trapped on and escape in a ship made out of a coffee can.
Squidward's Smug Snake rival, Squilliam Fancyson, gets two of these.
In the episode "Band Geeks", after setting Squidward up to fail for shits and giggles, seeing Squidward's band epically succeed causes him to stare in empty shock before HAVING A HEART ATTACK. Never has a Smug Snake been more brutally taken down.
In "House Fancy", Squidward's completely destroyed house is considered far fancier than his own and awarded several high honors for being 'artistic'. Squilliam's response is to sink to the ground and lay there crying his eyes out.
Krabs' megalomaniacal business rival Plankton gets several:
In the episode "The Algae's Always Greener", Plankton loses it when Mr. Krabs keeps on saying "And the next day." His reaction?
Plankton:(rips off his clothes, revealing a remote control underneath) It's not worth it! It's just not worth it! (He then regains his sanity) Goodbye everyone, I'll remember you all in therapy!(pushes button and vanishes)
In The Sponge Bob Square Pants Movie, he has one when SpongeBob begins freeing the Bikini Bottomites from his mind control helmets. He has a rough time handling it and calls out to Karen to do something, only to see she is being carried by the crowd. He then commands for King Neptune to kill SpongeBob, but he too is freed from his mind control. He tries to make a run for it, but he is then run over by the crowd while screaming in agony.
Dennis also has a bit of one in The Movie as well. He's a lot less cool and calm and a lot more prone to anger when confronting Spongebob and Patrick on top of David Hasselhoff than he was when tracking them down or his first confrontation. At this point, he was just crushed by a boot, and his loss of glasses and bandana shows more of his facial expressions.
Even when he wasn't completely evil, Krabs himself still had a few of these, namely in "One Krabs Trash", where he has a breakdown after realising the supposedly million-dollar #1 hat turned out to be worthless.
Squidward: What a baby.
While Nox in Wakfu was always pretty crazy, he snaps near the end of episode 26 after the Eliacube uses up all of the Wakfu he spent 200 years collecting in order to travel back in time to save his family — and only goes back twenty minutes. After a Big "NO!" and angrily demanding answers from the Eliacube (which he actually believes can talk), Nox almost shuts down. His breakdown is reflected by the fate of his creations: bereft of the Eliacube's Wakfu, all of them shut down and fall apart. The ending credits of episode 26 reveal that he was Driven to Suicide. Granted, he wouldn't have lasted much longer anyway without the Wakfu of the Eliacube to sustain him.
The villainous monster in human clothing V.V Argost had one of these in the final episode of The Secret Saturdays where he makes a planetwide broadcast for the world to yield to him as his army of cryptids are terrorizing the earth, and the Saturdays interrupt him by appearing with their own army. Argost's reaction was quite amusing.
In the 2003 Teenage Mutant Ninja Turtles incarnation, the episode "Insane In The Membrane" serves as a whole episode Villainous Breakdown for Baxter Stockman. His punishments for his constant failures was Shredder to reduce him to a brain in a jar, so he made himself a new body. Unfortunately, the new body begins to rot when he's in it. What is apparently hours or days later, the now half rotted and green-skinned Stockman begins having hallucinations about his childhood and his mother dying. He also promptly deludes himself into thinking April is evil, and responsible for everything wrong with his life. So Stockmanstein breaks into her apartment, takes her back to his lab, and yeah, more weird, oedipal stuff involving a cable car.
Robotnik to no one in particular: I really hhaattee that hedgehog...I Hate him. HATE HIM. HAAATEE HIIIMMM!! HATE! HATE!! HATE!!! HAAAAAATE!!!!!! ARRRRGAAAHHHHHHHHHHH!!!!
Brother Blood from Teen Titans had one that progressed over each of his appearances. In his first appearance, he was usually calm and controlled his students through trickery, fear and rage. By his last apperance, he was reduced to shouting in rage over Cyborg somehow being able to defy his control. It got even worse when Cyborg kicked his butt.
Slade's are more subtle, owing to his being The Stoic, but the climaxes of the season one and two finales both have him showing visible emotion (namely, anger) for the first time in those arcs, and when his normal cold-blooded cruelty gets mixed with that rage, the resulting actions push him even further into horrifying than he was already.
Vilgax from Ben 10 suffers one after being thrown into the Null Void and escaping. His previous motivation was steal the Omnitrix to take over the universe, even when he returned the first time that was it. This time he's gets a Twitchy Eye just thinking about what happened to him and is all out for revenge on Ben in addition to obtaining the Omnitrix, even if it results in the destruction of the universe. Ben even offers to surrender the Omnitrix without a fight if he gets the self destruct turned off and prevents the destruction of universe, Vilgax doesn't accept it because he wants revenge on Ben so greatly.
In Winx Club, Lord Darkar gets one when Bloom returns to normal via Prince Sky's kind words of "I love you", and returns the Ultimate power back to its rightful place.
Lord Darkar: NOOOOOOOOOOOOO!!! What did you do to it (the Ultimate power)?! Bloom: Sorry, but the Ultimate power's going back where it belongs.
And in response, he attempts to destroy and take his revenge on Bloom's friends and take Bloom back by spewing flames at the group, which Professor Faragonda and the other teachers deflect by putting up a magical shield around everyone, and he progressively continues spewing the flames at the shield in an attempt to break it and destroy everyone until the fairies unleash their convergence spell involving their Charmix, which allows them to conjure an expanding mass of light that causes Darkar to receive a massive Oh Crap! moment and scream "NOOOOO!!! This can't be happening!! NOOOOOOOO!! NOOOOOOOOOOOOO!!!" as the mass overwhelms him and sends him back to the chaos that spawned him where he will remain forever, and afterwards causes both his castle and Realix to start trembling and collapsing.
Valtor also gets one when he realizes that Bloom caused the box he kept all the magic he stole from all over the universe in to start leaking it out and returning said magic to their rightful places. He regains his Villainous Breakdown when Bloom cancels out his elemental clone attack involving the Spell of the Elements cloning four of the Red Fountain specialists by attacking him in his throne room from where she is fighting Prince Sky's clone.
Icy undergoes this after Bloom regains her powers. For the whole season she's a smarmy, psychotic Smug Snake; after Bloom gets her powers back she loses her cool, progressively screaming more and more until finally getting knocked out of the sky.
In "Sideshow Bob Roberts", Sideshow Bob is elected mayor and put on trial under the accusation that he rigged the election. Bart and Lisa drive him crazy by insisting that he was too stupid to rig the election and that his running mate, Barlow, was the real mastermind. Bob ultimately digs his own grave:
Bob: Only I could have executed such a masterpiece of electoral fraud! And I have the records to prove it! Here, just look at these (pulls out binders and floppy disks) each one a work of Machiavellian art! Judge: But why? Bob: Because you need me, Springfield. Your guilty conscience may force you to vote Democratic, but deep down inside, you secretly long for a cold-hearted Republican to lower taxes, brutalize criminals, and rule you like a king. That's why I did this: to protect you from yourselves. Now if you'll excuse me, I have a city to run. Judge: Bailiffs, place the mayor under arrest. Bob: What? Oh yes, all that stuff I did.
There's also Russ Cargill in the Movie who, after the dome is destroyed, turns a shotgun on Homer.
Frank Grimes. At the end of his episode, Grimes actually goes crazy and starts running around the power plant doing very dangerous things, pretending that he's Homer Simpson, before finally touching several live electric wires and being electrocuted.
Grimes: Extremely high voltage? Well, I don't need safety gloves 'cause I'm Homer Simp- (zzzzzzzzzzzzzzzzzz)
Gorillaz: Driven by greed and desperation, psychotic bassist Murdoc slowly became more unhinged with the Plastic Beach arc. He rants and raves aimlessly in his radio broadcasts and seems to be loosing his grasp on reality, and he no longer bothers to hide his criminal activity and blatant abuse of his "friend" 2D. The 'villain' term might be a little iffy, as Murdoc's still more of a Nominal Hero than anything, but he's definitely got some decay going.
Atlantis The Lost Empire: As Milo ruins his attempt to carry the crystal containing Kida to the surface, Rourke starts attacking him with an axe:
"I consider myself an even-tempered man; it takes a heck of a lot to get under my skin. But congratulations - you just won the solid gold kewpie doll!"
In "Mortal Folly", The Lich from Adventure Time starts laughing insanely when Finn is on the verge of destroying him — with a sweater no less.
He snaps for good in "Escape From The Citadel," as he's rebooted by the Guardian blood. He panics and starts screaming gibberish in an attempt to get it off, to no avail.
Daffy Duck has one in the Looney Tunes short, "Duck! Rabbit! Duck!" after being shot by Elmer Fudd for the sixth time.
Daffy: Shoot me again! I enjoy it! I love the smell of burnt feathers, and gunpowder, and cordite! I'm an elk! Shoot me, go on! It's elk season! I'm a fiddler crab! Why don't you shoot me?! It's fiddler crab season!!!
Elmer Fudd gets one in another Looney Tunes short, "What's Opera, Doc?": when he realizes that he had been duped by Bugs Bunny disguised as Brunehilde, he lets loose with Unstoppable Rage on the rabbit and summons the elements to help do him in.
Elmer: I'LL KILL THE WABBIT!!! AWISE, STORM! NORTH WIND BWOW! SOUTH WIND BWOW! TYPHOONS! HUWWICANES! EARTHQUAKES! SMOG!!!!
Happens to Miles Axlerod at the end of Cars 2 as a result of Mater exposing him as the villain behind the evil plot of the exploding race cars. He then goes crazy for a while before finally being forced to deactivate the Time Bomb he placed on the tow truck (it's voice activated, meaning that only he can turn it off properly) as a final attempt to kill him.
Happens in Regular Show to The Warden of the Internet in "Go Viral". After all her prisoners are freed, she flies into a psychotic rage, tearing herself out of the wall and going on a rampage.
Discord snaps when Fluttershy doesn't play along with his twisted mind games. He drops the Faux Affably Evil act and just brainwashes her with a huffy "Arrevederci!" Later, he actually gets terrified when he realizes he's about to be hit with the Elements of Harmony. His Faux Affably Evil act dissolves into fear as there's nothing he can do as the attack strikes him. Considering everything he'd done over the past two episodes has just effectively imploded right in front of him, this makes perfect sense.
In "Twilight's Kingdom - Part 2", Tirek is shocked that Twilight and her friends have magic again and finds himself completely overpowered by them.
Starlight Glimmer might have the most vivid one. Normally a Faux Affably Evil tyrant who runs on Sugary Malice and charisma, but once her plans fall apart, she becomes a Mood-Swinger between the friendly and psychotic rage before finally settling purely on the latter. She's still stuck in it when she returns at the end of the fifth season, but really goes into it when Twilight drags her into the future and shows her a barren wasteland caused by trying to stop the Sonic Rainboom.
Hexidecimal from ReBoot plays this straight for about all of five seconds, and then immediately subverts it. Her Medusa Bug turns all of Mainframe to stone, and Bob points out that she has made the entire place calm and predictable. As Hex is the poster child of chaotic behavior, this causes her to panic.
Hexidecimal: No! No! I must...I must stop it! Stop it all from going so very wrong! (Snaps fingers, undoes bug and walks off with a sly smile)
In Young Justice "Secrets", Harm's sociopathic villain act falls apart when he sees his sister Greta's ghost. The Sword of Beowulf rejects him when Greta removes the purity of his evil, and Artemis easily overpowers his clumsy attempts at close combat. He even drops the Third-Person Person speech.
In Anastasia when Anya smashes Rasputin's Soul Jar he completely loses it as his minions attack him.
Stinky Pete in Toy Story 2. "'Fair'?! I'll tell you what's not fair: Spending a lifetime on a dime-store shelf watching every other toy be sold! Well, finally my waiting has paid off, and no hand-me-down cowboy doll is gonna mess it up for me now!"
Lotso in Toy Story 3 is all smiles and unctuous charm, even after it's been revealed how nasty he is. Then, in their climactic confrontation, Woody brings up the subject of his previous owner, which gets Lotso increasingly riled until he finally screams "We're all just trash, waiting to be thrown away! THAT'S ALL A TOY IS!"
The Big Bad Wolf in Three Little Pigs, after his Fuller Brush Man disguise (or Jewish peddler disguise, depending on where you live in the world) fails. It also causes him to devolve back into an ordinary wolf.
Big Bad Wolf: By the hair on your chinny-chin-chin, I'll huff and I'll puff and I'll blow your house in!
In the Wallace & Gromit cartoon "A Matter of Loaf and Death", Wallace's washed-up bread spokeswoman turned baker-killing love interest, Piella Bakewell, apparently loses it after her plot to kill Wallace is foiled. She tries to fly away in the old Bake-O-Lite balloon, despite her growing too heavy to fly the balloon being the reason she was fired in the first place, and she babbles "They can't drop me, I'm the Bake-O-Lite Girl!" even as she descends into a pit of hungry crocodiles at the zoo, which is followed by the sound of Piella being eaten alive.
Miss Power has one in "The Rise of Miss Power" when WordGirl started to use nice words instead of mean ones, and she starts to lose her power. She then begins to stutter that she never loses, and she flees Earth, so that she wouldn't be defeated.
Dr. Two-Brains has one in the episode "WordGirl and Bobbleboy" when he's surrounded by bobblehead replicas of WordGirl, and he starts to lose it at how many WordGirls there were.
Yellow Submarine: The Chief Blue Meanie has a breakdown following Max's zinger after the Beatles have sung life back into Pepperland:
Chief: (calmly) Hark...the hills are alive... Max: (sung) With The Sound of Music...(Chief clocks him) Chief:WHO??!! WHO IS RESPONSIBLE FOR THIS??!!
He'd later go into a spasm and be placated with "nasty medicine."
Dick Dastardly throws a teary tantrum at the end of the Wacky Races episode "Race Rally to Raleigh" after failing to cross the finish line:
Dastardly: Oh, who wanted to win this old race, anyway? I DID!!! I WANTED TO WIN THE RACE!!! I NEVER GET TO WIN A RACE!!!
The Hooded Claw throws a tantrum at the end of The Perils of Penelope Pitstop episode "The Treacherous Movie Lot Plot". He had been filming all of the perils to which he subjected Penelope and figured that if he can't have the Pitstop fortune, he'll make a fortune himself with the movie. One problem: He never loaded film into the camera.
Cat R. Waul of An American Tail: Fievel Goes West starts out with all the grace and sophistication a Villain with Good Publicity needs. Even when the heroes come to take him down, he calmly sics his men on them. But once his trap has been exposed for all, this quickly gives way.
Cat R. Waul: Freeze, you miserable vermin! (starts shooting madly)
Justin Hammer in Iron Man: Armored Adventures started out as an eccentric, amoral and corrupted, but relatively civil and calm villain. Over the course of the story, however, his insanity becomes more and more clear, as he displays Ax-Crazy and Psychotic Manchild sides whenever he is having fun or when things don't go how he wanted. Eventually, "The Hammer Falls" involves him being blackmailed by a mysterious traitor; this causes him to go completely nuts, take down all his supervillain thugs out of paranoia, attempting to deliver a Zombie Apocalypse on Manhattan and losing the little sanity he had left.
Obidiah Stane experienced one as well when he found out who Iron Man really is.
The various characters of Invader Zim tend to fly into a rage when things don't go as they planned, with Zim himself being by far the most prone; in the episode "A Room with a Moose", for example, when Dib manages to foil the Irken's diabolical plan to send his classmates into a wormhole, Zim completely loses it and wails, "NO! NOOO, THE MOOSE HAS FAILED ME!"
This tendency, however, has been averted on the rare occasion: when another one of his plans (involving a robot copy of Dib and a monkey beating up the original), Zim screams "NOOO!!!" for a few seconds, but his anger peters out after a few seconds and he loses interest.
When cornered, Hakon turns on the Captain of the Guard, blaming him, and the two fight, falling off a cliff in the process.
City of Stone has Demona breakdown and cry at the end of it when the Weird Sisters confront her with her actions she gives the access code finish the heroes plan: Alone.
Xanatos distinguishes himself as not having one, he doesn't have a breaking point, unlike all the other show's villains, as he can bounce back from his defeats while keeping a relatively cool head. The closest he got to one was when all of his plans, schemes, In-laws, allies, and his Enemy Mine with the Gargoyles failed to stop Oberon, and even after that, he recovers enough to help work things out.
In Beavis and Butt-Head Principal McVicker seems to be in a constant one thanks to the duo's antics. Two good examples are his panicked race towards the school gym when he finds out the Secret Service has allowed the duo to join other students in asking questions to then-President Bill Clinton and his heart attack in the original Grand Finale when it was revealed that the duo weren't dead at all.
Many of the ghosts from The Real Ghostbusters went into fits of psychotic rage when they were defeated. One particular example is Karro Zans from the episode Ghostworld, who was driven insane by Egon Spengler outsmarting him and started using his powers to tear the amusement park he constructed apart and even growing to gigantic size while screaming "Prepare to die, Spengler!"
In Batman: The Brave and the Bold, Batman attempts to battle Equinox but realizes pure might won't save the day. Instead, he surrenders and makes him realize a crucial flaw in his plan to recreate time/space in perfect harmony: someone who isn't in perfect harmony can't make it. Equinox realizes that his hatred of the Lords of Order and Chaos outweight his desire for harmony and he realizes what he's doing is for nothing. He lets out a Big "NO!" before Batman knocks him into his portal, shattering him into pieces and scattered throughout time/space.
Bill Cipher has one in his debut episode in which he tries to kill the gang after his plans are foiled. As Affably Evil as he is, he puts on the rage better than a lot of the series' other villains. Subverted when he suddenly goes back to normal mid-battle and lets them win with grace, deciding they'll be useful to him later.
Bill Cipher: Do you have any idea what I'm like WhenI'mMad!?
Lil' Gideon also has one in the season 1 finale, where he pilots a giant robot in order to destoy the twins after realizing that the journal he took from Dipper was the wrong one.
From what little we've seen, Jasper seems to be undergoing this due to her individuality being worn away from being forced to stay fused with Lapis.
The Beast of Over the Garden Wall fame spends almost the entirety of the miniseries deathly calm and collected, only raising his voice off-camera to sing one of his bombastic songs. Then, when Wirt finally confronts him and realizes that the lantern the Woodsman has been carrying around actually harbor's the Beast's soul, he threatens to blow it out, causing the Beast to do this◊.