Beware the Nice Ones/Web Comics

"Fighter: Also, I can block any attack and kill anything that bleeds. Hint."
 * White Mage from 8-Bit Theater shows this after rebuilding a city and its inhabitants from destruction at various hands (although mostly Black Mage) only to have the city yet again annihilated at the hands of, apparently, Black Mage. Feeling distressed and angered (also mostly due to Black Mage, although Fighter had an unwitting hand in it), she changes her robes and begins bestowing her mediocre evil upon the world for a couple comics until changing back after a strange talk with Fighter.
 * One guest strip had Black Mage push her over the edge with one too many pickup lines, whereupon she began chasing him with a chainsaw.
 * A better example would be Fighter, the nicest, friendliest, ditziest character in the comic who has a very potent Berserk Button whenever his friends, especially Black Mage, are threatened. He went into an Unstoppable Rage when Black Mage was killed, fought a fire demon to a standstill after she, and this comic.

"Thief: Yes, it is a good thing. Leaving him to rot would be wrong. Red Mage: So very wrong. Fighter (holding up a sword): Kind of chainsaw wrong. Thief: Okay, good thing we're all on the same page then!"
 * Thief and Red Mage better watch themselves... they almost made that mistake again.

"Joyce: "This is for the thousands of little comments that are hammered into me every day! "Stop giggling, Joyce!" "Put down your dumb toys, Joyce!" You can only take so much... Until you snap.""
 * While he is in no way a nice one, a case can be made for  given that
 * El Goonish Shive has Grace, super cute pacifist who just wishes people wore less clothes. You can tie her up, torture her, even tell her you are going to use her for a breeding program. Make her believe you have hurt one of her friends though and there is no power on Earth or beyond that can save you.
 * To not quite as potent an extent, Elliot. He's extremely nice and by default helpful. Of course, mocking Tedd or any of his friends changes things.
 * And now, we learn, Noah. Not only do his girly looks hide inhuman strength and speed, but his particular speech patterns are a deliberate focusing mechanism to keep control of an otherwise short temper.
 * Rikk, the leader of the Science Fiction Club in Fans!, is as nice, gentle and forgiving a man as you're ever likely to meet. However, during a storyline in Fans! which sees a bitter ex-boyfriend of Alisin's blackmail her into joining him, while simultaneously attempting to destroy the fan-club and replace it with a new, darker version - Rikk is finally pushed too far, and beats the ex-boyfriend to a pulp before someone stops him from going too far.
 * Piro from Megatokyo is an example, as a group of perverted otaku voyeurs in a restaurant found out. This is more obvious in Piro's online alter-ego Piroko, and associated wallpapers/tshirt with a cute girl carrying a big gun, and the phrase "Ph34r t3h cute ones".
 * Ping from the same comic could be an example, as well. She's normally sweet, cute and caring, but get her angry and she proves to have the strength to uproot a street lamp and use it to beat a giant monster into submission.
 * "That was very rude, Mr. Turtle!"
 * Nice people in the Walkyverse usually get this. Joyce is a prime example. So is Walky himself, for that matter. Not to mention Amber... this list could go on for a bit.

"That is IT. EVERYBODY OUT. You are DEAD SERIOUS."
 * Lemmy in Fanboys is a genuinely nice guy, but woe be unto anybody that says Nintendo is a kiddy system.
 * ANGRY CLOWN MODE.
 * An impact to the head can do it. When running from a crazed feral crab in the Beach Episode, he crashes headfirst into a sign, which triggers the aforementioned Angry Clown Mode, allowing him to handily demolish his tormentor.
 * Sam has a moment of this when blackmailing a ninja in this this Sam and Fuzzy strip.
 * Surprisingly, Hannelore, Questionable Content's resident Woobie. Not to mention her dreams.
 * Out of Ctrl+Alt+Del's "Four Players" side story, Player Three, the yellow one, is the one to be careful of. Sure, he starts out as the Butt Monkey of the other three players, each more sadistic than the next, but has been known to snap while put under extreme duress. Player Two fell victim to this, as Three grabbed him and slammed him against the wall until he ragdolled all while shouting, "STOP IT<". He then came to and tried to apologize for what he just did.
 * In Dan and Mab's Furry Adventures, it's Mab.
 * For that matter, Dan. While normally a nice guy with a vague career of adventuring behind him, recent events have shown just how dangerous he really is after being pushed over the edge. It's not pretty.
 * It's not as explicit now that element of her character seems to have been phased out, but Lorenda Soulstealer used to eat people who annoyed her, and she still acts enough like a demon to terrorize a group of papparazzis into leaving Jyrras alone even after he gets declared "This Year's Most Eligible Bachelor". Otherwise, though, she's a cheery, good-natured cow whose not offended in the slightest by comments on her chubbiness.
 * In Bun-Bun's continuing feud with Santa Claus in Sluggy Freelance, Mrs. Claus is the one pushing for the two of them to just let it go, but she's also the more dangerous Claus when she has to be. Bun-Bun acknowledges her as a better shot than Santa, and it's her who.
 * Gilgamesh Wulfenbach. Just... Gilgamesh Wulfenbach.
 * Here too.
 * To explain, he's a genius who never even bothered to build a death ray, and who will put up with massive annoyance to avoid killing people he neither likes nor respects, but when an enemy army really gets in his way, he smashes it in about five seconds.
 * He skipped straight through 'death ray' and went on to 'heavy artillery'.
 * "If I let everyone I thought was an idiot die, there wouldn't be many people left."
 * Incidentally, it is not a good idea to push Agatha too far either.
 * Higgs might seem like a stoic who though Made of Iron and perfectly capable of fighting does so calmly, is not exempt from this either after.
 * Tarvek isn't exactly a "nice one", given his Chronic Backstabbing Disorder, but the one and only time we ever saw him be violent, it was a staged fight that both parties got a little too into.
 * Liza from Tonja Steele is a good example, as she's usually a sweet-natured schoolteacher. Some of it is explained when we meet her parents.
 * Elan in most of Order of the Stick; naive, sweet-natured but ditzy Cloudcuckoolander. Elan in strip # 594, after Smug Snake Kubota poisons his lackey Therkla (who was in the midst of a Heel Face Turn) and she dies in Elan's arms; Unstoppable Rage-driven Badass. It's only Kubota's swift-but-slimy opportunism that prevents him from getting a severely lethal ass-kicking at Elan's hands, and even then he still gets a black eye for his trouble.
 * Black Eye? That's a black eye to you? He got.
 * There's also the Monster in the Dark. While he (she? it?) has not yet gone past the breaking point, strip # 475 suggests that making the monster angry is an idea so stupid that it borders on Too Dumb to Live.
 * The Sakana brothers embody this trope like a glove in different ways. Taro is a former delinquent with a fondness for knives who will unleash hell on those who cross him and especially those who dare hurt his little brother. Jiro isn't nearly as violent, but he can be just as scary (if not moreso) with just a Death Glare and a stone cold voice, as seen when he kicks out with just few words.
 * Quentyn of Tales of the Questor gets his sword stolen, and in the course of retrieving it gets arrested multiple times, mugged, shot at, dropped through a roof, stripped naked in front of a crowd of toffs (and his childhood crush), and then violently beaten and tossed in a dumpster. He promptly girds up his loins and proceeds to utterly wreck not one, but TWO street gangs singlehandedly and literally pull an entire building down around their ears... and would have REALLY torn them a new one had the city guard not intervened.
 * The Raccoonan nation topped that in the companion strip, Quentyn Quinn, Space Ranger. In there, the horrific cannibal species, the Kvrk-Chk, made a public show of what they would do the Raccoonan race when they ate a number of them on camera, The Raccoonans retaliated the next day by
 * Do no try to get uppity with Charles the counselor at Camp Calomine because he'll rip the pay-phone off a utility pole while doing his best impression of the evil Father from Codename: Kids Next Door.
 * Plant Woman. It's one thing if you've only built *two* machines of death and destruction. The first law of robotics is thrown out the window completely when you announce the third.
 * This strip from The Adventures of Dr. McNinja plays this straight.
 * Faen from Drowtales. She's a rather shy, sensitive girl, who also happens to be a powerful Empath with less than perfect control over her powers. Strong fear/anger cause Power Incontinence and since she's a projective Empath, people get hurt.
 * Calvin/Freckle from Lackadaisy Cats. Shy, scared, and gullible, but put him in a life-or-death situation and give him a gun...
 * And Ivy too, as Rocky soon found out.
 * Just about every one of "The Dragon Doctors" qualifies for this. Goofball wizard Sarin has a dark criminal past and has immense transformational powers when pressed. Kili the sweet and sensitive shaman can transform into a snarling werewolf due to her recent contraction of lycanthropy. Even their mostly-quiet leader Mori, a magical scientist, has combat options, and has invented a magic beam that can blow your clothes and weapons away.
 * Guy, from Mushroom Go. Guy is a literal shy guy that never speaks, happily dedicated to his work as the crew's nurse, cook, and housekeeper. Though afraid of hurting other people, he's proven himself a decent fighter--with scalpels and chainsaws.
 * Magic and Physics has SPDA who seems like a genuinely nice person (being maybe the only one in the strip), but all hints about his back story suggest something that could have easily cost lots of lives.
 * Gamzee Makara from Homestuck, generally the Cloudcuckoolander of the trolls, recently
 * Don't make  angry.
 * John totally fails to invoke this trope. Behold John getting angry:
 * John totally fails to invoke this trope. Behold John getting angry:

"Arkady: Do you know what that was Luke? That was exactly one second of my overdose experience when we were fifteen. If you ever do something like this again, I am going to give you five minutes of that."
 * Subverted in The Inexplicable Adventures of Bob. Bob is usually remarkably effective at getting things done and defeating enemies, and he hardly ever throws a punch; but it turns out that, idealism aside, part of the reason he isn't a fighter is that he isn't very good at it. (Galatea, on the other hand...)
 * Iceland from Scandinavia and The World. This explain its all.
 * PIFFANY. Seriously, guys, vex not the diabetes-inducingly-sweet cleric. She's basically made of so much pure, distilled goodness that it gives her Reality Warper powers, in addition to the awesome spellcasting Dungeons and Dragons clerics are normally capable of. So on the rare occassion that she does get angry with someone, it inevitably ends badly for them.
 * Drive: Nosh is usually a happy, Big Eater Omnidisciplinary Scientist. But if you're a Tesskan, and you disrespect his captain (or presumably anyone he considers a friend), he will curbstomp you and nineteen of your buddies.
 * Big Ears in Goblins is a genuinely Lawful Good paladin who occasionaly strays into Honor Before Reason but avoids Knight Templar and Lawful Stupid. Oh, and he doesn't like it when you throw rocks at his catatonic friend.
 * The Oswald Chronicles has the eponymous Oswald, a mild-mannered and polite gentlemouse. He prefers to talk things out instead of resorting to violence. Hurt his friends, however, and...
 * In retrospect, this covers Mirth from Voodoo Walrus as her first appearance involves her erupting from the belly of a Hobo Jesus and then summoning a flock of fingerbats to murder his hobo zombie followers.
 * Julie, from Our Little Adventure when  Her bubbly, happy personality vanishes and is replaced by something violent and scary, complete with Creepy Monotone and Hidden Eyes. In the next page we see her rapier embedded in the Minotaur's skull.
 * People in the Dominic Deegan world get so hung up on Luna's emotional problems that they always forget that she is a master of Black Magic.
 * Ashton in Winters in Lavelle spends half of the comic looking like a scared, lost puppy. However, when people start threatening him (or Kari), he manages to fight a random Gard, Xan, and
 * The Freak Angels are, in the words of Alice, kind of crap when you get right down to it. All of them have psychokinetic powers, and can do some serious damage all by themselves without lifting a finger. Out of the group, Arkady is the most gentle (except possibly Connor), and on a good day, she's a slightly unstable Cloudcuckoolander, and a Mad Oracle to boot, but a Friend to All Living Things. But then Luke tries to Mind Rape some poor girl, and Arkady takes direct action.