In the Ace Attorney manga, Raymond Spume becomes enraged when Sparkle Land publicity assistant Julie bites her nails, believing it to be a bad habit and unprofessional to do it in public. This ultimately proves to be his undoing.
Thomas Spitzer gets angry when someone questions his expertise on spiders.
One played for laughs: don't steal MISAKA 10032's nightvision goggles. She's got an assault rifle in her schoolbag and unless the thief is Last Order, she WILL shoot to kill.
And the original Misaka Mikoto has a few as well. On the comedic side, we have Kuroko trying to peek at her panties and Touma continuously defeating her in fair fights. On the dramatic side, we have anyone hurting her clones, who she considers sisters. The first time this happened, she unleashed a whirlwind of iron sand, and when that didn't work obliterated forty research facilities in three days.
There's also the matter that catching Accelerator red-handed during the Level 6 Shift project was the only time Mikoto ever tried using her signature railgun attack on a human. Granted, he No Sell'd it without effort but it does not change the fact that she just tried to use massively lethal force against a living target.
Touma's entire class has one: making their teacher Komoe cry. For example, all of them were unmotivated and unwilling during the athletics festival... until they overheard another teacher insulting Komoe and calling her school and students trash. They went on to cream that teacher's class, despite being massively outmatched in esper powers. (Komoe herself doesn't understand why they're pushing themselves so hard.)
For Touma, don't you ever harm or threaten innocent people, no matter the reason. Don't you try to use a Freudian Excuse, Dark and Troubled Past, or Motive Rant, no matter how sympathetic, to justify lashing out at the world. He'll just prove you a Hypocrite and punch you into next week.
Seiri Fukiyose does not like it when people complain about bad luck. She works hard and encourages others to do the same. To her, luck is just a loser's excuse. Ironically, she has no idea that Touma's bad luck is real.
Shutaura Sequenzia lost her father in a plane crash that only killed him, but the event was declared a miracle for the minimal loss of life. For this reason, she doesn't believe in miracles and gets pissed at anyone who even mentions the word "miracle".
In the harem comedy manga Ai Kora, Maeda tends to go ballistic on those who ridicule or harm the girls in his harem, especially if they threaten their "perfect features" (like a delinquent who nearly knocked out one of Sakurako's flawless blue eyes, or a salesman who preyed on Yukari's self-consciousness about her "bullet-train bustline" with dodgy "breast reduction" bras).
Tina and Mayu have a shared Button in anyone trying for Kaoru's affection.
Even if a bit scary, Kitano of Angel Densetsu is an All-Loving Hero. He will not fight back (not that you can actually hurt him)... unless he thinks a girl or someone in his True Companions are in danger. Luckily he will not hurt youmuch, just be prepared to be knocked out for an hour or two. And hope you're landing on a soft surface after he blows you three meters away. And forget lifting anything heavier than a tissue the day after. Make it a couple of days maybe.
Titans in general are one giant Berserk Button for Eren Jaeger from Attack on Titan. As one can probably imagine, he's got some pretty big rage issues.
He goes off on one guy who makes an insensitive remark about how the Titans should have eaten more people so there would be fewer mouths to feed — shortly after Eren had just watched his mom get eaten.
Seeing one of his comrades get eaten during the Battle of Trost is what drives Eren to charge madly into the fray. No, it does not end well for him. Or anyone with him for that matter.
Mikasa tends to lose her cool whenever Eren is threatened or harmed. One notable example is when Levi beat Eren up during his trial to actually save his life. She was prepared to attack the in-series World's Strongest Man until Armin held her back. However, her anger can get the better of her, such as when she blindly attacked the Female Titan for capturing Eren, forcing Levi to save her and he got injured.
Greece from Axis Powers Hetalia is a calm, easygoing Heavy Sleeper until you put him in the same room with Turkey. And if you want to see the fireworks really go off, just position Turkey anywhere remotely close to one of his cats or Japan.
It also doesn't take much to tick off Russia. If you thought Stalin had it rough...
His sister Belarus is already a Creepy Child. Attract Russia's attention to yourself? Uh, better RUN AWAY.
Don't comment on how attractive Austria is if Hungary's around. Especially if you're France. Actually, for that matter, don't even comment on it if Austria's around, particularly if you're France.
Do not mess with Liechtenstein. Switzerland will not be pleased. By the same token, don't talk smack about Switzerland's pajamas. Liechtenstein spent fifty two days making those things, dammit!
In Azumanga Daioh, don't tell Chiyo-chan's "dad" that his face resembles that of former prime minister Mori. Especially don't tell him that he's not a real cat. Also don't show him anything that's red.
Firo of Baccano! is quite self-conscious about how young and feminine he looks and reacts quite strongly to having it pointed out. Reactions have varied from snarking back, making death threats, or, in one case, breaking the offender's fingers.
In Bakuman。, Takagi becomes enraged if someone suggests that Mashiro is weighing him down or he should find someone else, even in times when Mashiro believes he's the weak link.
Miura takes it personally when Mashiro or Takagi indicate that they don't trust him or they trust someone else's opinion more.
Battle Royale protagonist Shuya Nanahara's best friend, Yoshitoki, is extremely protective of the orphanage's overseer, a pretty young woman whom Yoshi has a secret crush on. When he finds out that the Big Bad raped her, he completely loses it and charges at him. It does not end well for him.
Also, anyone who waltzes in and starts shooting when Revy and Eda are at the Church of Violence "had better damn well be prepared to go to war," as the scumbags chasing the title character of the Greenback Jane arc found out the hard way. Eda in particular does not look kindly on anyone putting a bullet in the church.
Balalaika is often called "Fry Face" behind her back. Almost no one calls her that to her face, and with good reason. Her real Berserk Button, on the other hand, as evidenced in the Vampire Twins arc, is anything happening to her men. She will come down like the wrath of God on anyone who messes with her men, even if she has to call in the Vysotniki to do so.
Hansel and Gretel do not enjoy being yelled at or struck, though in their case it's less of aBerserk Button and more of a "We want to kill you" button, as Verrochio and his men found out the hard way.
And the female employees of the Lovelace family of Venezuela will not react well to anybody attacking or kidnapping a Lovelace. Since either of the two maids could give the Terminator a very bad time... it's just better not to even think about trying it. And if you actually manage to kill one...PRAY FOR MERCY.
Revy's button about Rock got hit again when Jane mentioned possibly seducing Rock if Revy didn't want her banging Benny's brains out all the time. The result is Revy getting really creepy as she relates her sexual experiences in prison and threatens to make Jane her bitch.
It takes a lot to get Rock good and pissed, but wantonly abusing people he considers innocent (such as Yukio) will bring out his worst language and drive him to violence.
Blue Exorcist: Rin is not a terribly placid person at the best of times, but calling him a demon or insulting/threatening his family really sets him off. Yukio is similar, and also really doesn't like getting his glasses broken.
Busou Renkin: Papillon utterly despises being called by his real name by anyone other than Kazuki. He was also not too pleased to find that Kazuki had apparently given up his humanity to become a Victor-like being after having fought Papillon, to prevent him from giving up his humanity to become a homunculus.
In the manga Cafe Kichijouji, Jun, a younger effeminate boy, snaps into a violent manner if anyone makes the unfortunate mistake of saying that he looks like a girl.
Sakura Kinomoto in Card Captor Sakura is usually nice enough to her brother Touya, but the second he calls her 'Monster' she grinds his foot into the floorboards.
Oh, that's nothing. Hurt her friends? Imitate her Missing Mom to mess with her? Make her lose a gift from her crush? You're dead.
Chrono Crusade has a more serious example (that's particularly noticeable in the manga version): Chrono is known (depending on the translation and whether it's the manga or the anime) as "the Slayer of 100/1000/100 million." How'd he get that name? Well, in the manga, he tried to rescue some of his fellow Sinners and found them killed by enemy demons. He picked up the body of a small child, staring in horror, then snapped, killing the number of demons he was said to have killed in one short, bloody, rage-filled battle. This happens at least a few other times, particularly in the manga: if he's threatened or someone he cares about (PARTICULARLY Rosette) is hurt, his demonic nature takes over and things get very violent, VERY quickly.
Shinka from Chuunibyou Demo Koi ga Shitai! hates any mention on adolescent delusions (or "chuunibyou"), because she herself was a pretty serious victim of this. On the other hand, she also deeply resents Sanae's insult to her as a "Fake Mori Summer," "Mori Summer" being the her delusional identity.
Lelouch Lamperouge's Berserk Button is people threatening or harming his little sister or his friends. Not a problem in and of itself, but he has... troublewith restraint once the button's been pressed. What got Lelouch to really flip his lid was when his "brother" shot Shirley and, despite Lelouch's strongest efforts, he could not save her. It didn't help his sanity that she gave him a most romantic "good bye" speech.
Rolo also goes nuts when somebody mentions Nunally.
Mentioning Orange in front of Jeremiah Gottwald is asking for either a major thrashdown or a drastic shortening of your life span. Seriously, don't do it. Until he joins Lelouch during R2 episode 14, after discovering the reason why Lelouch became Zero.
Hyoma Aoi from Combattler V lost his parents when he was barely a toddler, and was raised in an Orphanage of Love. So, harm/kill a child (even if it is an animal cub) or leave him/her/it parentless, and he will go nuts before beating the crap out of you.
Cowboy Bebop: As shown in "Jupiter Jazz (Part I)," it's a terrible idea to call Spike by the name of his rival Vicious. He ends up going berserk and beating up an entire gang — whose leader survives, only to toss himself into the back of a garbage truck.
Spike: You think I'm Vicious? YOU DON'T KNOW WHAT VICIOUS IS!
The suggestion that girls should date a boy for Yanagin.
For Yoshitake's older sister, the fact that she doesn't have a boyfriend — despite the fact she's just 18.
Kazuya Ryuuzaki from Daimos is a nice, kind guy... but when you piss him off, he goes downright nuts. And he is a karate champion... Threatening his beloved Erika? Bad idea. Killing children in front of him? VERY bad idea. Getting people executed for no reason other than you are a racist nutjob? Ashtoundingly BAD idea. Miwa found out about that the hard -and very painful- way.
If there is one thing guaranteed to piss Light/Kira off, it's suggesting that what he is doing is wrong or evil. In fact, it's a very good way to wind up with your name in the title notebook.
As far as Misa is concerned, Light is hers, and she will notstand for any other woman getting close to him.
Matsuda lost all respect for Light the moment he insulted the memory of his late father, Soichiro Yagami, whom Matsuda had looked up to, near the end of the series, which combined with him trying to kill Near with a scrap of the notebook led to Matsuda going berserk and shooting and nearly killing Light.
It is highly recommended you don't tell Buttercup/Kaoru from Demashita! Powerpuff Girls Z she looks cute in a skirt. Her reaction is not pretty.
Also Bubbles/Miyako hates to see mistreatment to animals of any kind, as the Rowdyruff Boys find out. Except Mojo, obviously, and a bunch of these monkeys who admittedly didn't deserve Bubbles/Miayko's sympathy with the way they were acting. Though she did feel some sympathy for him when she found out why he is the way he is. But Mojo immediately does something evil to get rid of that sympathy.
All 3 of the girls, especially Momoko/Blossom, will get super-mega-pissed when you steal their food, make them leave lunch, or just prevent them from eating in any way. And to a lesser extent, make them miss sleep and they will get angry.
Trying to hurt Ran in Detective Conan will cause Conan to do everything in his power to bring the culprit down, even if an Action Girl like Ran can handle things perfectly fine on her own. He may be trapped in a little boy's body, but he's got an extremely sharp mind as well as very powerful tech-equipped sneakers and he won't hesitate to use them to bring you down for even looking at her wrong.
The alternate happens if harm comes to Conan, her father Kogoro, or even to her mom Eri and her best friend Sonoko: if one of them is in danger, Ran won't hesitate to karate kick anyone in the chest.
Also, if you're a Yandere or a Cute Psycho, don't kill/harm anyone when Shinichi/Conan's around. If there's a specific kind of culprit that he hates, it's those two. Specially if Ran has been caught in their plans.
Kogoro is a Private DefectiveButt Monkey, but there are two ways to make him make him show some competence. The first one is to threaten people like Conan, Eri, or Ran — and ESPECIALLYhis little girl Ran. The other is someone double-crossing, tricking, lying, or downright betraying him; finding out that one of his True Companions from college was not only a murderer, but that they had killed another member of his group of friends had Kogoro completely fuming like few times it has happened in the whole manga.
Please do NOT dismiss friendship in front of one Sonoko Suzuki. Even worse if either you look down on one of her friends, or you do it towards your own friends. The girl's a Brainless Beauty but she strongly believes in those she cares for, and even if she can't fight she'll do what she can to protect them and she'll expect you to appreciate your loved ones too.
In The Devil is a Part-Timer!, Rika Suzuki lived through the Kobe Earthquake and lost some of her friends to it. She does not like people asking her about the event.
He had another one when he was evil: being called weak. Do not, do not, DO NOT call him weak. EVER. He casually (and gruesomely) killed one of his allies for doing so.
The anime version of Dinosaur King has a Running Gag where Zoe insults Ursula by calling her an "old lady", which leads to Ursula's Berserk Button being pressed. In fact, she can even hear her calling her an "old lady" from any number of miles away, no matter how far off she is from her.
Zoe: Hey, old lady! Ursula: Arrrggghhh! I'm not an old lady! Got that?!
Kei and Yuri have only one official code name: The Lovely Angels. Calling them the Dirty Pairto their faces — or suggesting that two college-age girls can't be all that dangerous — will earn you a punch in the face.
Plus, what they will do if you actually are the individual that they have been hired to bring in.
Or if you're simply unfortunate enough to be in the immediate area once they're finished their mission.
In some cases, "the immediate area" may be the ENTIRE PLANET — or on one occasion, several star systems.
Anna and Uni Puma from Dominion Tank Police. Not like they're not psychotic enough to begin with, but if anyone makes reference to their humiliating origins as "love dolls," the body count is going to go into triple digits.
Shizuo Heiwajima from Durarara!! hasn't been mentioned yet? Do NOT test his patience. Just... don't. He punched a guy so hard that the poor guy's clothes flew off as he was launched about 20 feet into the air. It gets even worse if you're being nosy about his adored brother Kasuka. Mentioning Izaya is another great way to ask for an early death. Vending machines will fly.
Also works in a triangle for the Power Trio of Kida, Mikado, and Anri...mess with any of them and one or both of the other two will come running to kick your ass. And then take into account that these are two gang leaders and the human host of a demonic sword respectively.
Perhaps a tribute to Evangelion, Renton in Eureka Seven goes brutally psycho over his opponents at the end of episode 20. Unlike Evangelion, however, it's his deadly combination of his love for Eureka, his hatred towards Holland and frustration with his immaturity that makes him berserk instead of the Nirvash. The result: Blood, a dismembered arm, and a horrific scream, much like Shinji's in The End Of Evangelion.
Whenever Eureka comes to harm, Renton will go berserk at the one who's responsible as evident in the movie version.
Daigo Ikari of Eyeshield 21 has a Berserk Button that goes off whenever someone insults one of his teammates, regardless of whether the insulting party was joking or not, or if he could get injured in the process (for example, he at one point dives off the stands to attack Onihei after he had called Otawara an idiot). The result is often that his own teammates have to restrain him with chains because he'll break free if they use rope!
In this situation Ikari was frankly just being too sensitive; Otawara is an idiot. In any case, the fact that he goes completely nuts whenever he hears someone badmouth his school or its football team is the reason he's two years behind in school; He was sent to a juvenile detention center after one of his "incidents."
NEVER insult anyone who stands up to Gaou around him. He will kill you.
Monta has a berserk button of being called a monkey.
Do not insult Sena in front of Chuubou unless you want to get knocked down.
Sena is usually a pretty scrawny kid that you can pick on a lot. He's used to it. Agon learned the hard way that, when you keep calling his hard working team a bunch of trash, he'll come at you on the field with murderous intent.
Hurting Kid is the best way to enrage the normally emotionless Tetsuma. For that matter, calling Tetsuma an idiot is enough to make Kid drop his lazy uninterested fascade really fast.
Messing with Panther's sweatband which was given to him by his beloved grandmother made the normally Nice Guy attempt to throw a punch at his racist couch.
Fairy Tail: The Phantom Lord guild pressed it....a lot by attacking three of their members and bolting them to a tree with their guild insignia on one of their stomachs. This prompts a full on, rage fueled, assault on Fairy Tail's side.
Do not hurt Mirajane's little siblings.
Or vice-versa with Elfman.
Nor come between Erza and strawberry cake.
And threatening or insulting Jellal may be a bad idea as well. Just ask Midnight.
In the latest Filler arc, they manage to defeat the Big Bad and her artificial dragon by smashing Natsu's Berserk Button several times in a row in order to overload the dragon thing (which was using him as a power source).
Another one of Natsu's Berserk Buttons is hurting a member of your own guild!
Do not ever say that Dragons don't exist when Natsu is around.
Do NOT threaten Gray in Juvia's presence.
And hurting one of their friends is pretty much a Berserk Button that they all have.
Especially when the person on the receiving end of that harm is Lucy or Wendy. Congratulations, Team Raven Tail, you did both. I hope you cheaters like high voltage.
For that matter, NEVER attempt to inflict an injury that disfigures a mage's guild mark no matter who that mage is. On top of adding insult to injury with regards to the victim him/herself, guildmark-disfiguring injury or any threat thereof is a DIRE insult to the guild to which the victim belongs.
And God help you if you insult Fairy Tail in front of LaxusDreyar. Flare Corona learned this the hard way when she threatened Lucy with guildmark-disfiguring injury in their Grand Magic Games fight.
Call Jagi by his own name and not his little brother's when he's trying to blacken his name? You're dead. Anything involving a "little brother"? You're dead. Gloat that you raped his girl to death? You're dead. Recoil in horror at his disfigured maskless face (courtesy of said little brother)? You're really dead.
Toki may be a pacifist and is dying from radiation sickness, but if you harm any innocent people, you will learn the hard way that he is just as deadly as Kenshiro himself.
Despite his cold demeanor, Mikagami Tokiya from Flame of Recca HAS one Berserk Button: Call him a girl, a she-man, or whatever Gender Bender insult to him and the best thing you can hope for is a death cold stare from him (which is thankfully what he usually does so far...)
Franken Fran: If you value your life even a little, NEVER fuck with professor Amatsuka, or Gavrill and Fran will come after you. Even if you manage to avoid getting slaughtered by the former, the latter still has her own methods of punishment.
One of the two main characters of Freezing, Satellizer El Bridgette, is unique in that she has two different berserk buttons...
The first one is defeat. If you ever try to force her to admit defeat, whether she's slashed or even her throat slit, she'll never do it. Instead, she will fight on doubling and tripling her speed and power, even if she is unconscious.
The second one is sexual intimacy in any way, especially rape. Any kind of even slightly intimate contact will cause her to immediately lash out with incredible force, with the exception of the other main character Kazuya Aoi, who she can sense on instinct is pure of heart. However, if you try to torture her by either attempting to rape her or have someone else come close to raping her, PREPARE TO DIE. She will become a being of pure killing intent, and unless you are extremely lucky, she will end you. In fact, her killing intent was so absurdly strong that the local 'head fighter', who was far more powerful then Satellizer, was simply turned into a frightened kitten after looking at her, hiding behind her own subordinate.
Fruits Basket: Messing with Tohru around Kyo, Yuki, Hanajima, or Uotani is a really, really bad idea. Especially considering that Kyo and Yuki are both extremely skilled martial artists, Hanajima is probably capable of killing people with her powers, and Uotani is an ex-delinquent.
If you hurt Rin, Haru will go Black on you. Being incredibly annoying isn't advisable, either.
Kaname Chidori is hardly the calmest of characters, but the one thing that really sets her off is the possibility that her precious grade levels are in danger. Such as the discovery that Sousuke left her notes back in his apartment on the day of a test. Cue Sousuke being physically hurled onto the road in order to (barely) stop a taxi in time, so they can drive back and get them.
Fuck with Kaname and Sousuke will kick your ass with his rage-poweredHumongous Mecha.
Fushigi Yuugi: Do not call Tamahome "Obake-chan." It won't be wise to hurt or threaten Miaka or his family either. Too late for the latter, though.
Also, looking at Suboshi's brother the wrong way is utterly wrong. Suboshi killed Tamahome's family when he thought the Suzaku Seishi had murdered Amiboshi, after all.
The words "Nuriko" and either "gay" or "pervert" are not to be used in the same sentence.
Another baddie forfeited his life when he nearly killed her brother.
I dare you to try to harm Setsuna Higashi from Fresh Pretty Cure! in any way. In fact, I double dare you to try to brainwash her. If you do so, prepare to face the wrath of Love Momozono. That's right, I'm talking to you, Nayuta Kita.
In the same series, Setsuna herself gets pretty upset when someone who's still in Labyrinth brings up her past as Eas. As she put it to Westar, "I am no longer Eas!"
Other Cures are this way, too. In Yes! Precure 5, Nozomi and Rin when dreams and her siblings are threatened respectively. Tsubomi finally got her game face on when the first monster she faced smashed a bed of flowers she landed near. And when a member of the Quirky Miniboss Squad tried to seriously hurt Nao's little brothers & sisters, shewentcompletely berserk.
If you want to live in the Future Diary metaverse, there is only one rule that must be obeyed: Do not harm OR get too close to Yukiteru Amano. For if you do, Yuno Gasai, the most terrifying Yandere in existence will come and get you. And considering this girl is an absolute killing machine with a higher body count than anyone else in the series combined, you are definitely screwed.
Game X Rush: Yuuki's Berserk Button initially appears to be knives, but is actually anything that might threaten "Yuki-san".
Motoko Kusanagi from Ghost in the Shell: Stand Alone Complex who is generally professional and stoic, gets exceptionally pissed off when a mini-mecha wearing goon tries to kill her by attempting to crush her skull under his "foot"...
Sodoko gets angry when people break the rules, act in a way she considers arrogant, or call her "Sodoko" (although for the latter, she seems to make an exception for her friends and fellow hall monitors Gomoyo and Pazomi).
Momo gets rather annoyed when she misses, or gets called "Momo-chan" by Yuzu. She gets sincerely upset when her teammates express a belief that they won't win, or that they don't care whether they do, since she knows the school will get shut down unless they win the tournament.
Surprisingly enough, Miho has one in Little Army. When Emi, one of her friends, declared that she hated Miho's older sister Maho despite never even having spoken to her before, Miho lost her temper and yelled that she hated Emi.
Do NOT betray Golgo 13 and do NOT stand behind him. It's dangerous.
A once-off rival assassin's was being called a "deformity".
Great Teacher Onizuka: Do not call Onizuka trash. Ever. Be prepared to have your back slammed to the floor by a fantastic martial artist if you do.
Making fun of Mobile Suit Zeta Gundam's Kamille Bidan's Embarrassing First Name sets into motion his joining La Résistance—Jerrid's snarky comment that it's a "girl's name" causes Kamille to leap over a barrier and attack him. Keep in mind that Jerrid is an elite, uniformed Federation soldier with other Federation soldiers.
Mobile Suit Gundam Wing: If there's two things Heero Yuy and Zechs Marquise/Millardo Peacecraft share, it's the ability to use the ZERO system, and the sheer amount of destruction they can cause, just because you had to threaten Relena Peacecraft, Heero's best friend/love interest and Milliardo's little sister, respectively. Even an underground, for-all-purposes impenetrable fortress won't stop the former from kicking your ass.
The usually ladylike, quiet and gentle Relena has more than one button of her own. Try harming someone in front of her? She'll shout "Go Through Me!". Insult, mock, harm or kill her adoptive father? She'll tell you off or try to shoot you. Keep repeating that war is the best thing since sliced bread? She'll slap you and verbally wipe the floor with you.
Turn A Gundam: The Gundam itself is Corin Nander's berserk button—he will instantly fly into a rage and try to destroy it. Even a paper-mache parade float gets this response. Since he's implied to be a survivor of Gundam Wing's Wing Zero, he has a fanatical desire to destroy any white Gundam.
Mobile Suit Gundam 00: Do NOT say anything bad about one Neil Dylandy within the earshot range of Tieria Erde.
... nor should you mention Celestial Being in front of one Louise Halevy.
Also, touching Setsuna's Gundam with intent to damage it is a sure way to antagonize him, as demonstrated in his first "fight" against Sergei. Additionally, a sound drama has Hallelujah's bravado screwing up a battle and damaging the Exia; Setsuna does NOT sound pleased during debriefing.
And while terrorism makes anyone mad, it's really not good to discuss it in front of Lockon in S1. He gets more pissed than anyone's ever seen him when Tieria makes tasteless comments about a bombing and pulls a gun when he learns that Setsuna was one as a child, even though he's Setsuna's Big Brother Mentor. His successor and twin is more sanguine about it in S2.
Mobile Suit Gundam AGE's Flit Asuno already hated the Unknown Enemy / Vagan for killing his parents, but when Desil Galette killed Yurin L'Ciel, Flit lost it. Any mention of the Vagan gets him mad—any suggestion that they're human makes him snap, even if it's the rather reasonable suggestion that Vagan prisoners be treated as POWs instead of just killing them after surrender.
Also, harm or touch Mashiba's little sister and things will end badly. No ifs, ands or buts.
The Melancholy of Haruhichan, in one of the episodes, had a scene of Achakura wondering if she had have her own stool or chair, then, after Nagato puts down a baby rocker beside Achakura or puts Achakura in the baby rocker note Due to Achakura being in her chibi form. respectively, Achakura thinks, "Yeaaah, something like that." and "Yeaaah, something like this." respectively, before taking out her anger at Nagato by yelling " THAT'S NOT A STOOL! THAT'S A BABY ROCKER!" and " I AM NOT A BABY!", repectively.
Achakura is also dead serious about Nagato not going to sleep, and every single time Achakura notices Nagato's laptop, Achakura attacks Nagato and yells, "Go to sleep!" In the Halloween episode, Nagato opens up her laptop, and Achakura proceeds to destroy the laptop and yell, "GO TO SLEEP!"note As Achakura yells at Nagato, Nagato is shivering in fear.
Also, there was this scene in one episode where Nagato, out of complete curiousity, shuts Achakura shut in the jack-in-the-box thingy. That was the result of getting scolded. So please, for the love of God, DON'T mess with Achakura. Even when it comes to jack-in-the-boxes.
In Hayate the Combat Butler, Nagi goes apeshit when Hayate discovers her self-made manga and calls it a "picture diary." She boots him out of the study, but he mistakes it for her kicking him out of the mansion.
She does it again when she suspects Tama tore up her beloved manga. She locks him away.
Also, causing Maria to remind people that she's only 17.
Probably the biggest Berserk Button in the story though, is Hinagiku and any character making note of her chest size. Grabbing it (however unintentionally) automatically triggers it, though just referring to it has to be done at least twice. She's taken out an army of volleyball robots, and the one controlling them, just because he made the comment twice, with implied use of only volleyballs as well.
For Issei, it's harming anyone in his Battle Harem. You especially do not want to make Rias cry. You especially do not want to threaten the size of his Harem's breasts.
The girls, in turn, all have one for trying to harm Issei. After his apparent death, Rias creates a spell powerful enough to erase the target from existence, just to use on anyone who pushed that button.
Rei Miyamoto from Highschool of the Dead has a Shidou-shaped one. The bastard flunked her out due to their fathers' radically differing political beliefs, and as a result, she despises him.
History's Strongest Disciple Kenichi: One has to start wondering why all of Kenichi's opponents say they're going to kill/hurt Miu when that has consistently been shown to be the one thing that will make him stop sucking and actually kick some ass.
Calling him a chicken has a similar effect, although it isn't quite as strong.
Don't even THINK about harming his sister Honoka. Property will be damaged.
Akira Hongo, the "God Fist" karate specialist of the antagonist Yami group, has a strong sense of honor, and has respect for others despite being technically a bad guy. But do NOT insult the memory of his late disciple Sho Kanou or else he will go Tranquil Fury and stab his hand through your skull. Silcardo Junazard just barely avoided being Impaled with Extreme Prejudice this way, although his signature mask got destroyed as a result.
Kamishiro Yuu from Holyland loses it after one of his friends is beat up by a gang and goes on a gang-hunting rampage. Given that the manga is fairly realistic in its treatment of street fights, this is quite the feat of endurance and strength.
Don't ever mention spiders to Kurapika. Don't show him a spider. Don't expose him to anything involving spiders at all, ever.
On a more serious note, anything involving the Phantom Troupe, the group that slaughtered his clan for their scarlet eyes, will set Kurapika off in a big way. When one sorry bastard during the Hunter Exam tried to intimidate him by claiming to be a member, Kurapika saw right through his claim, but was still pissed enough to one-shot him in a blind rage.
Don't even joke about killing Killua if Illumi is in earshot.
Do not hurt Gon's friends. Gon broke Illumi's arm when he found out Illumi broke Killua's spirit causing him to fail the Hunter Exam. Neferpitou sealed his fate when he killed Kaito.
Sesshoumaru's only displayed a Berserk Button twice in the manga: when Inuyasha pitied his injuries on the battlefield and when Mouryoumaru insulted Kagura's death. The latter upset him so much that he broke Tokijin over it, endangering his own life in the process.
As soon as Naraku's manipulations are laid bare from forcing Sango and Kohaku to try and kill each other, his taunts about Inuyasha's powerlessness and compassion, and what he did to Kikyou in the past, the normally sweet and well-intentioned Kagome explodes with rage. The result is the instant purification of the miasma that has killed an entire castle and which was slowly killing them, as well as tearing Naraku's body to shreds, something none of the group had been able to achieve at that point. Kagome's friends are absolutely stunned by both Kagome's rage and her level of power.
"Would you shut up?! I'M GETTING ANGRY!!"
A few characters in Is This a Zombie? have at least one. For example, don't casually tell anyone to go die. Eucliwood has experienced death every time she brought someone back from the dead, but fortunately offenders have been known to merely get a slap on the wrist from her for the effort. Also, do not abuse Eucliwood's powers, or Seraphim will be so furious she'll leave her footprint on your face.
Josuke of JoJo's Bizarre Adventure will go from polite doormat to rampaging berserker if anyone dares insult his hair. This includes his allies. In one particularly humorous scene, his opponent (who is currently bedridden from severe racing injuries) plays off of Josuke's moral nature to keep himself from getting attacked... only to end up insulting his pompadour. Josuke gets around beating up the helpless by using his powers to heal the fellow, and then beats the man to a bloody pulp and throws him out a window. He gets better, though.
Wham, one of the Pillar Men in part 2, will instantly attack anyone who steps on his shadow, including his superiors, who take no offense to the attack because is speed and power are an asset, and they can heal it anyway.
Keroro Gunsou has Giroro. Don't mess with Natsumi if you want to live. It doesn't even matter if he's anywhere nearby sometimes.
Kill la Kill: When it comes to Ryuko, making light of her father's death will bring her to a boiling rage. When she finally discovers his murderer, Nui Harime, who does this all the time, Ryuko goes completely berserk and her blood overheats in anger, causing Senketsu and her to turn into a disfigured monster.
Ryuko is also not a fan of perverted guys trying to steal a peek at her bathing or changing clothes.
Don't touch Inumuta's laptop, or he will flip out at you.
Nui Harime is usually bubbly and happy, with a grin on her face at almost all times. However, if she is caught by surprise ( in Isshin Matoi's case) or if she finds herself outclassed ( in his daughter Ryuko's case), she will really start losing it.
Don't call Mikisugi's mecha the "Dotonbori Robo", or he'll insist that you call it "DTR".
In the Kirby episode "Hour of the Wolfwrath", the frontman says that Wolfwrath (Chilidog in Japanese) doesn't take too well to training.
King Dedede: That Wolfwrath monster of yours better not wreck my castle! This ain't no doghouse! Frontman: I'm afraid Wolfwrath doesn't take too well to training, Triple D. He's kind of a hot dog, and if you try to break him, you'll get burned. (laughs) King Dedede: Huh?! It'll attack me?! (The frontman laughs even more)
Tia gets incredibly mad when a mamodo keeps flipping her skirt to take a peek at her panties. This is enough for her to discover she has a spell fueled tby The Power of Hate.
In Kotoura-san, Manabe is very protective of his girlfriend Haruka. Mock, belittle, or just straight mess with Haruka in general and prepare to have Manabe's wrath brought down upon you.
Whatever you do, do NOT threaten to sell Chieko's (from Kuragehime) dolls, even if it's to do something like finance an anti-eviction fund. Don't mess with the settings on her sewing machine, either.
In Lost Universe, do not rag on Kaine's rag. (Calling his cape a rag is a good way to get a lightsaber to the face.)
In Love Hina, Motoko's older sister Tsuruko is a graceful Onee-sama. But please, PLEASE, don't tell her a lie. Not even Motoko can get away with being creative with the truth in front of her "Ane-ue". In fact, Motoko being the liar made the deal even worse.
Do not touch Takuto from Macademi Wasshoi in an even vaguely lascivious manner when Suzuho is around, or she'll whip out her Superpowered Evil Side and try to beat the crap out of you (especially if your name is Tanarotte, who, to be fair, can give the punishment right back).
Macross Frontier's Alto Saotome is prone to eye-twitching or shouting every time someone brings up his more feminine characteristics. This only encourages his friends — especially Michael (who popularized his "Princess Alto" nickname not only across the school, but also in fandom).
The third season adds more cases: Don't hurt Vita's friends either; abducting Subaru's older sister or Nanoha's adopted daughter, and destroying Caro's home or threatening to do so is a bad idea as well, as all of those have led to an Unstoppable Rage.
Yuuno gets quite upset whenever someone like Chrono calls him a familiar, or makes a "joke" about his ferret form.
Don't mess with Negi's students in Mahou Sensei Negima!. More importantly, do not tell him you just put him through hell and wasted months of his time and made him take up black magic for a fight he had no chance of winning. Possibly an invoked trope considering Rakan just got done revealing himself to not be a moron and here he is acting like one again. Also, he wants Negi to fight his best.
Also, never tell Negi that you're the one responsible for the stuff that happened to him in the past... like, well, torching his hometown and petrifying everyone. Wilhelm and Kurt Godel discovered this the hard way.
Considering the diary reading Negi's mind after finding out what happen turned black with thoughts like "Do Not Forgive" and "Kill Them" its a good thing for Chisame's epic Bright Slap to snap him out of it or things would of gotten bloody.
Haruka tends to get set off by people breaking rules, and, in the manga, by her plans to replace the Orphan Resistance Unit with the Ori-Hime unit running into problems, and people making fun of her large forehead. In the anime, insulting Yukino is another of her Berserk Buttons.
Yukino is typically soft-spoken and good natured, but can become quite angry if people act dismissively toward Haruka.
In Mai-Otome, Shiho becomes enraged if someone calls her "Maki-maki." Arika finally gets angry with Tomoe when she makes fun of and expresses relief toward Erstin's death.
Wolfgang Grimmer from the series Monster has an alternate personality ("the Magnificent Steiner") that functions as one of these. It activates whenever he is in extremely stressful situations and invariably results in a body count. Ironically, when he commits his most extreme act of violence, he remarks that he didn't need to invoke his alternate personality and that he really was just that angry.
Nagasumi Michishio from My Bride Is a Mermaid is generally pretty unassuming, but the moment you threaten his wife Sun you're in for a world of hurt. Remember the last episode, where pointing a gun at her empowered Nagasumi to catch a freaking bullet with his teeth? And then punch a guy so hard that he transforms spontaneously?
Nabari No Ou: Don't ever call Yoite cute or emo; it will be the last thing you ever do.
Cause any harm to Gau and Raikou will mutilate you until you're unrecognizable.
The title character in Nadia: The Secret of Blue Water easily loses her temper over any trivial issue whatsoever, to the point where it nearly harms her growing relationships with Jean, Marie, Grandis, and Nemo. It takes a long time for Nadia to learn to control her temper.
Ikuto of Nagasarete Airantou, if told anything is "absolutely impossible," will get it done with twice the speed and four times the effort.
Madara/Neko-sensei from Natsume Yuujinchou doesn't like it when Natsume is in danger or hurt but the one time that Natsume was shot was the first time we truly see him furious.
In addition, don't speak dismissively of humanity or threaten the lives of those Kazuma believes to be under his protection if you are at all attached to your vital organs.
Multiple characters in the Neptunia series have these:
Plutia, don't you dare hurt her friends; then she transforms into her sadist alter-ego and whips the living hell out of you.
Vert, don't insult her breasts, seriously, she will send you flying through a building.
Blanc, don't insult her lack of breasts or threaten her little sisters; then you get either the hammer (normal form) or the giant axe (transformed).
Nepgear, don't you dare hurt her big sister, she will use her giant gun/sword to slash and blast you to pieces.
Uni and Noire both go homicidal if the other is hurt; and both of them threaten to tear Anonydeath apart for spying on Noire.
No. 6: Whatever you do, don't insult the Dogkeeper's mom. Or suggest that Nezumi become a prostitute. You will suffer endlessly.
Never harm Nezumi. Or you'll get a bullet to the brain from Shion.
Nezumi doesn't like it if someone messes with Shion either.
Kaoru Orihara from Oniisama e... is usually the Only Sane Woman of her school's idol group, but never, ever mistreat Nanako (and her friends) and Rei or neglect your own health when she is around. Aya and later Fukiko (for the former) and Mariko (for the latter) learned about this the hard way.
Speaking of Mariko, don't abuse Nanako, abandon her or make fun of her parents' divorce, if you wish not to get slapped and yelled at or to get your arm slashed with a box cutter.
Fukiko looks calm and graceful, but she's got some big buttons of her own. You should neither make any allusions (even if accidental) towards her onesided love for Takehiko, nor speak openly against the Sorority. Expect some huge retribution if you do.
In the anime, if "Borgia" Ogiwara wants some answers to her questions, you better give them to her.
In Oto x Maho, Kanata is a guy who transforms into a magical girl to fight. He also has many Berserk Buttons.
Whatever you do, DO NOT CALL HIM A GIRL. If it is your first time making the mistake, and you're on his side, then he'll explain it to you. Other than that, he will launch a massive magical attack at you.
If there's one thing he hates more than being called a girl, it's being stalked. He will often get a killing aura whenever he sees someone he knows in a place that they CLEARLY followed him to. If it's someone who knows he's a magical girl and there's no one around, he will blow them up with magic.
He also hates pictures and models of himself, and will confiscate them. If you do not hand them over, he'll hurt you. To be fair, he'll hurt you either way.
Tamaki also gets pretty ticked when someone (usually the twins) makes a move on Haruhi. Except for Kasanoda, where he went into a Heroic BSOD!
Tamaki doesn't hesitate to threaten to beat a couple of thugs to a pulp because he thought they hurt Haruhi. Lucky for them there was a camera crew right there, and violence would not be good publicity for the Host Club.
Don't hurt someone Haruhi cares a lot about. In the manga after the story enters darker territory, the Host Club bursts into the Suou's company building. Haruhi demands to see the company chairman, Tamaki's grandmother, because of some recent events like her making Tamaki quit the Host Club. And being the Plucky Girl that she is, she doesn't let up either, shouting and making a scene in the front lobby until Yuzuru shows up.
Kyouya cares very much about his friends, especially Tamaki. He blackmails the Newspaper Club who were planning to try to destroy the Host Club with fake stories, beating them at their own game. Later in the manga he rips Tamaki's father, Yuzuru a new one for more or less using Tamaki to steal the company from his mother, and get Tamaki's mother, Anne, to Japan, without thinking of Tamaki's own feelings. Also, he will expose you and have you arrested if you sell fake products for money and he finds out about it.
If anything, Haruhi acts as the trigger for the host club. Don't hurt her or the rest of the club will come after you and make you suffer A Fate Worse Than Death.
Xerxes Break from Pandora Hearts, who is normally Obfuscating Stupidity, gets very serious VERY quickly if one of the few people close to him is in danger. Namely, Sharon and Reim/Liam.
In Popcorn Avatar, any mention of harming his sister Mafuyu is guaranteed to set Kurando off. Later on, this extends to Lisa as well.
In episode 2 of the Pretty Sammy OAV, Tenchi mentions to Bif Standard that his software is slow. At that comment, Bif goes into a lengthy rant, feeling that he had insulted his software, and Tenchi, Sasami, and Misao quietly escape while he is still ranting.
RanmaSaotome hates it when his masculinity is questioned (or calling him ugly in his female form), and only partially due to his Gender Bender curse. Particularly in the anime, calling him a coward also triggers this. He doesn't think much of people attacking innocent bystanders, either.
Surprisingly, given Ranma's rabid defense of his masculinity when questioned, there was a situation in the manga where his female appearance was insulted based on looks, and he responded like he would have with any of the other comments.
Akane Tendo goes nuts if you point out she's got a comparatively plain figure compared to Shampoo, Ukyo Kuonji or even her fiance. Or that she's utterly hopeless at any traditional feminine activity, such as cooking, cleaning (tends to break the tools/what she's cleaning), laundry (rips, stains or shrinks clothes), tea ceremony, etc. It doesn't help that her fiance is exceptionally good at most of these.
Don't insult Akane Tendo anywhere in Ryoga Hibiki's hearing. He will make you suffer for it.
Speaking of Akane, don't hurt her. If you try, Ranma will be violentlyunhappy with you. Attempting to kill her will only make things worse.
Never, EVER take or harm one of Happosai's "treasures" (i.e. bras, panties (both of them usually stolen), voyeuristic pictures, etc.). Sometimes he'll just get his revenge through pranks like tacks in your shoes or ordering mass amounts of delivery food in your name, but other times? He will KICK. YOUR. ASS.
Corporal Randel Oland from Pumpkin Scissors displays this. Normally lighthearted and puppy-friendly, when he finds himself in mortal danger, he reverts to the role he served in his previous military as a one-man killing machine specifically designed to take out tanks all by himself. This coincides somewhat with the idea of an Unstoppable Rage, but his behavior in this "form" doesn't look angry so much as it looks completely cold, determined, and calculated. Nonetheless, the end result is the same and most would be wise not to incur his pavlovianly conditioned wrath.
The same applies to all the protagonists. Hurt their friends, and you won't be waking up feeling pretty in the morning.
Special mention for hurting Tsukune (in a seemingly fatal manner) in outer Moka's presence (a la ep 1.9); inner Moka WILL emerge (rosary be damned) and hand you your ass.
Inner Moka doesn't like to be touched. As Tsukune found out the hard way very early on in the second serialization, Double Standard does not apply here even if he is her boyfriend.
Rozen Maiden doesn't have much of this, but Suigintou is more messed up than she usually shows. While sadistic and brutal, she rarely drops her cool and composed manner, antagonizing Shinku with an alluring, self-confident voice occasionally interspersed with a soft evil laugh. This goes away when Shinku calls her "junk", whereupon Suigintou completely loses her cool and starts screaming "I AM NOT JUNK!!!!" Her power does significantly increase, but that's not doing her good most of the time.
Rurouni Kenshin: Himura Kenshin is a generally calm, friendly, kind-hearted, patient and forgiving man... unless you decide to do something dishonorable and stupid, like needlessly harming (or worse, killing) innocent, weak and/or defenseless people. Especially when the people being hurt or threatened are women and children. He won't hesitate to beat the crap out of you. Hurting his any of his friends is also something that's sure to piss him off. And while he won't kill anyone, you'd probably wish he had by the time he's through kicking your ass if you so much as think about hurting his girlfriend Kaoru...and all this is AFTER he manages to overcome that nasty little split personality problem of his, because if you had decided to push him over the edge back then, he really would've tried to kill you.
Kid Samurai Yahiko, being Hot-Blooded, flies off the handle when being called a kid or being addressed as "Yahiko-chan". (Though, hilariously, he once got pissed off at Tsubame when she sort of joked that he was finally growing up.)
AoshiShinomori is on his way to Kyoto when he passes by the graves of his buried Oniwabanshu comrades...with four of Makoto Shishio's mooks having a picnic near the gravestones. He tells them not to desecrate the graves. One of the mooks spits on one gravestone as an insult. All four get butchered very bloodily for their trouble.
Mentioning Enishi Yukishiro's dead older sister is a good way to set him off, especially if your name is Kenshin. Because Kenshin killed her, albeit unintentionally.
Seems as though, even in the first season when Usagi was still learning to be brave, that if someone messed with her best friends, she would spring into action blindly, regardless of the risks. In the first season, it was anytime someone tried to harm Naru that the button was seemly hit. Nephrite nearly found this out first hand when he tried to steal Naru's energy in the mall. And what caused Sailor Moon to spring into action for the first time? She had heard Naru's distress call in a rare use of her extra-sensory hearing devices in her odangos, and when she got there? A monster was holding her hostage. What followed was the first In the Name of the Moon speech in the entire series, and when the monster ordered her personal army of zombies to attack, Sailor Moon proceeded to rush in and counter without thinking of any proper strategy.
The mere mention of the word "family" seems to set Koromo off, as she grew enough anger to cause a blackout upon hearing it. It's presumably related to her deceased parents.
For Kanna of Saki Shinohayu Dawn Of Age, even laying eyes on her hated rival Hayari "Hayarin" Mizuhara is enough to send her into a rage.
Oniwakamaru, from the second episode of Samurai Champloo, kills anyone who calls him a monster (usually based on his physical appearance).
Samurai Deeper Kyo has mellow bishie Yukimura, who will tolerate familial treachery, attempted assassination, kidnapping, and many other horrible things without his trademark smile even flickering. Even if you try to kill him, he won't lose it. But hurt or disrespect one of his beloved ninja followers, and he will slice off your ass and hand it to you on a platter. While still smiling.
Threaten Yuya, and Kyoshiro will punch Kyo out of the way and fight on his own.
Later, threaten Yuya, and Kyo will turn into a DEMON GOD and shove a sword up your ass.
In Sangatsu no Lion, Rei is furious when Gotou speaks badly of his adoptive sister, especially since Gotou is the one that's currently dating her.
Yakumo from School Rumble is quiet and calm...until you start talking smack about her dear sister Tenma. Then it's ON!
Because his persistently failing challenges towards Yutaka, being second is his berserk button—this includes his name, which literally means "reciprocate-the-second."
Never ever give Lena from Shamanic Princess the impression that you're either abandoning or betraying your loved ones. Or she'll thrust for your blood like no one else would.
Sakai Yuji who is really a Nice Guy at the start of the series but even then he in the light novels didn't take it very well when Wilhelmina attempts to make Shana give him up by force, Yuji very nearly kills her with Blutsauger. Then he become Snake of Festival's vessel in which he is more than capable to beat you up or worse he could make you cross cross Despair Event Horizon just by talking.
You will think Shana and the red oni of Battle Couple is the one who has this, but compared to Yuji and considering her personality it's mild in comparison.
Do NOT refer to Faust VII's wife and partner spirit Eliza as a "puppet" or a "doll." He's usually calm and arrogant to an inhuman point, and takes all the insults thrown at him with stride... but the moment you insult her, he will go into an Unstoppable Rage and KILL YOU.
Never put ANY of Yoh's friends in danger, unless you want him to come at you and cut you down to size.
In Shin Mazinger, Kouji snaps when Boss and his goons insult his grandfather Juzo one too many times. He promptly beats the ever-loving crap out of Boss, and would have seriously hurt him if Kouji's soon-to-be girlfriend Sayaka hadn't interrupted to tell Kouji that his grandfather was in real danger.
In the original Mazinger Z, Kouji also reacted badly if you insulted his grandfather, hurt Sayaka or harm innocent people... and Sayaka reacted furiously if you insulted her skills or made Stay in the Kitchen statements directed at her (needless to say, Kouji pressed her Berserk Button constantly). Tetsuya from Great Mazinger— Kouji's adoptive brother — also got MADLY enraged if you slighted his skills... But Duke Fleed from UFO Robo Grendizer topped all of them. Nothing got his blood boiling like mentioning the Fleedian genocide and the deaths of his family. And when a Vegan commander or soldier taunted him with it... let's say it did not end well for him.
And in the Shin Mazinger Zero manga, you do NOT try and harm Sayaka. Otherwise, Kouji... will not be nice to you.
Don't mess with Rin from SHUFFLE! in range of Nerine's hearing. She does not approve. As she says, fortunately, you don't have to be hospitalized... because she'll try to kill you.
In Skip Beat!, never mention the name 'Fuwa Sho' around Kyoko, or vengeful spirits will haunt you.
In Slam Dunk, Shohoku ace Rukawa shall NOT be interrupted when he's sleeping. Expect physical damage if you do.
Rukawa (to Norio Honda): My name is Rukawa Kaede, I'm a first grader, and I will NOT forgive the idiots who wake me up when I'm sleeping. *beats the crap out of Honda*
Also earlier in the series, if you ever say 'Basket' or something that sounds like that in the vicinity of Sakuragi, expect yourself to pass out after he headbutts you. When he gets into the basket team, he switches it to being mocked or told that he's not good enough. As well as harming his friends and teammates.
Their captain and leader, Takenori Akagi. Insult basketball in front of this Genius Bruiser and you'll see exactly how much of a Serious Business the sport is for the guy.
His sister Haruko has some of her own. Please, never EVER disappoint her. Or be rude towards her friends.
Please refrain from hitting women in front of Miyagi Ryota, especially Ayako.
Lina Inverse of Slayers has a slew of these, and most of them serve as a base for the series' comedy. The biggest one is calling out her small bustline - Pokota calling her a demon "who spreads flatness" was enough for her to throw an amplified Dragon Slave spell at him. Along with this are not giving her food when needed, her 1,001 nicknames (and her sorcerer guild's title, "Lina the Pink"), not getting rewarded, Gourry's stupidity, calling her short...the list goes on.
Gourry's sole berserk button (aside from trying to steal his family heirloom, the Sword of Light) is harming Lina.
Anything in regards to Zelgadis' chimeric body will set him off, comedic or not. When he finds out from his great-grandfather that he can't get rid of it, he loses his mind. Alternatively, when its usefulness is pointed out, he gets pissy and moans about it.
Sonic X: Way to go, Eggman. You destroyed Amy's lucky bracelet that she made for Sonic from the seashells she collected in Episode 9, made her react with the phrase of "I don't believe it!" and made her cry. Then she flew into a rage and screamed "Now you're gonna PAY!!!" before proceeding to pound both you AND your current Robot Of The Week into submission. That's where you realize that you're screwed. Yup. Not a good idea. Don't ever mess with Amy or you're done for.
Also, Cream has a chao named Cheese. Cheese is Cream's friend, but sometimes, when Cheese is mentioned to be Cream's pet, Cream goes mad.
Also, don't pull a prank on Ella. Bokkun learned it the hard way.
Hime Makita from Sora No Manimani gets very tense about her hair, and did not hesitate to knee a fellow student when her old nickname of "Drif" (as in "The Drifters," a Japanese rock 'n' roll comedy band with fluffy hair) was brought up.
Want to push Death The Kid's Berserk Button? Just show him anything that's too asymmetrical. Case in point, in his first appearance, he goes completely bonkers just because a mummy in an otherwise perfectly symmetrical pyramid wasn't symmetrical himself.
Likewise, insulting his father is also a bad idea.
Shinigami and Kid share (appropriately enough) the Berserk Button of anything threatening their idea of order. Shinigami is considerably more lax about it than his son, but when pushed can cause even more damage, as shown when Asura was revived.
Do not hurt Mikuru while Kyon is present. This man did not shy away from attempting to punch Haruhi for it.
Kyon gets a little scary if any of his friends are threatened.
Turned Up to Eleven in Kyon Big Damn Hero, when Kyon hung someone outside a window as retribution. To be fair, they had just tried to shove Tsuruya out of it. Haruhi had a similar reaction later on, when Kyon was shot.
Don't look up Mikuru's skirt, or Haruhi will be very pissed off with you, never mind that it may have been an accident.
Eto Kai from Switch! gets extremely violent if his life or the lives of those he cares about (Hal particularly) are in danger.
For that matter, don't hurt Kirito in front of Asuna. She doesn't take lightly to that either.
Both of them don't want you to hurt Yui, their adopted daughter ingame.
Simon from Tengen Toppa Gurren Lagann has two Berserk Buttons: Kamina and Nia. Mess with either of them and he'll go after you to the ends of the universe.Literally in Nia's case.
Kamina's button? Depriving him of fanservice. At least in the uncut English dub.
Kamina: YOU WANT TO KNOW IF I HAVE A PROBLEM?! YOU TOOK THE ABSOLUTE HIGH OF THE HUMAN SPIRIT, THE VERY ESSENCE OF A MALE SOUL AND STUCK IT INTO THE DIRT, SMACKED IT AROUND AND SMASHED IT! I'LL FOLLOW YOU BASTARDS THROUGH THE FIERY PITS OF HELL AND KILL YOU A MILLION TIMES OVER!!!
If you want to genuinely piss Kotetsu Kaburagi off, disregarding human life - any human life - is the way to do it. He gets understandably angry when Maverick holds his daughter Kaede hostage. Maverick's last ditch attempt to escape is to put a gun to Kaede's head. The presumed-dead Kotetsu comes out of the shadows and punches Maverick in the face.
In Tona Gura, calling Hatsune "motherly" means a Tickling Hell for whatever poor soul did so.
In Musou Kakyou: A Summer Day's Dream, Reimu flips out and flies into a rage in a "This Cannot Be!" kind of fashion when she sees that her donation box (which she needs for an upcoming festival at her shrine) has gone missing. Also, later, Patchouli's Berserk Button gets pressed when she gets hit in the face by a book thrown by Aya (after which she gets knocked down and says her Catchphrase in "Mukyu!"), and she screams "You... YOU PEOPLE!" Several scenes later? She's busting out ROYAL FLARE.
Vash the Stampede from Trigun gets extremely upset if a single person gets killed, even a bad guy. In episode 12 of the anime, Monev the Gale decided to blow up a city block whilst chasing Vash, and instead killed dozens of townspeople. He was promptly confronted by a VERYangryVash, complete with Glowing Eyes of Doom. It went downhill for him from there; indeed, Vash almost crossed his moral line but experienced a morality check and managed to stop himself.
Fai from Tsubasa Reservoir Chronicle is a pretty laid back guy, but get him to stab the girl he calls his daughter, and he's going to blow shit up. Also, he absolutely refused to kill his father figure Ashura-ou at first, but when Ashura stabbed Kurogane... Well, he got really mad, and resolved to kill him.
Also, though Kurogane is usually pretty grumpy, he gets especially crazy if you threaten any member of the quartet (except perhaps Mokona), or his lady-of-liege Tomoyo-hime.
In Ultra Maniac, if you ever harm Nina's pet cat, you'd better hope her friends restrain her, or you'll wind up deader than he.
Utawarerumono has a few instances of justified anger inciting fury, but the two truest berserk buttons belong to Touka and Hakuro, the former humorous and the latter resulting in a "holy shit" moment.
Warrior Cats: Don't mess with BloodClan members. Scourge will rip your throat out.
Wolfen Crest: Don't you dare compare a gang of common Chaotic Evil delinquents to the noble and much-maligned wolf in front of Inugami, he'll give you a Death Glare and an talking-to the likes you've never seen!
Also, don't talk to Akira Inugami for more than five minutes. A certain gang leader gets rather... testy, when Inugami confides in someone other than him. Also, don't insinuate that Inugami's a Nice Guy around that certain gang leader either.
Yu-Gi-Oh!: Don't threaten Seto Kaiba's little brother. Just don't. It is not a good way to blackmail him, only a way to guarantee him making you pay.
Do NOT mess with Yugi or any of his friends unless you want an ancient Egyptian spirit challenging you to a deadly game with even deadlier consequences once you lose.
Good job, you either threatened, knocked out, or desouled Yugi Moto! You have just sentenced yourself to one of two fates:
Is the Puzzle anywhere near Yugi? Pharaoh's coming out to play. note He can do this entirely at will, like his first encounter with Teya, his duel with Pegasus, and instances in the Duelist Kingdom arc. You're fucked, end of story.
Wait, the Puzzle is far from Yugi? Wait until Joey finds out. The longer he knows and the longer you're still conscious, the closer the probability of him tearing you a new asshole becomes one.
Speaking of Jou, do not call him bonkotsu ("mediocre" duelist), dog, monkey, or other insult of inferiority. Do not deny him entry to your tournament to spite him. And do not threaten or harm him and/or his friends, or else he may just go on a Roaring Rampage of Revenge. He does not take disrespect well.
Also, do NOT tell Kaiba that Yugi lost a duel to someone. If you are on a phone, the volume of his voice will break the receiver. As he puts it
Kaiba: No one deserves that title but me!
In 5D's, it's apparent that to press Yusei's button, all you have to do is threaten to destroy Neo Domino City. Placido found this out the hard way and was left in pieces by the time Yusei was done with him.
Also in 5D's, do NOT call Jack 'former King' or anything similar. Also, don't steal his Ramen.