Berserk Button

Don't be fooled with people whom seemingly possesses mild temper, as certain insult turned out causing them releasing an apocalyptic and fiery temper no matter how good they able to maintain the composures!

Berserk Button is the term about the part of an individual's personality where they would lashed out (usually violently) should proper insult inflicted on them. It doesn't matter how good they maintain their temper, as there would be some limitations in the situation where they need to maintain their patience or composure over the situation that potentially provoke them to release their anger. The trigger for them to release their wrath could be anything, from weight issues, family, or even something that looked trivial in your point of view.

Once triggered, they would instantly goes ballistic, flying into a screaming, frothing, sometimes apocalyptic wrath where should his ballistic rage was on extreme level, it would be wise to stay out of his/her way until his/her mood swings surpass where it's safe to apologizing.

Example

 * Don't call Alvin and Simon's brother Theodore the fatty ratty, or they'll go all beat you into pulp.
 * Marty McFly insists, "Nobody... calls me... chicken!" - a behavior he only starts to exhibit in the second film.
 * In Space Jam, Lola Bunny goes into a basket-busting frenzy whenever anyone calls her "Doll."
 * In 2002's Spider-Man film, during his Villainous Breakdown, Green Goblin recklessly hits Peter/Spidey's Berserk Button as he lashed out on the hero when he says exactly what he's gonna do to Mary-Jane after he kills Peter in retaliation of failed to have him forced to watch either MJ or a trolley of children died in front of him, which turned out to be his undoing.
 * Luke's Berserk Button is turned out to be his revealed sister Leia, who is the only family he has left: When he is trying to keep his anger in check to avoid falling to The Dark Side in the fight against his fallen father Vader, Vader threatens to convince her to the Dark Side should he never embrace The Dark Side. As result, Luke ended up retaliate by cutting the fallen Jedi's arm and left him on his mercy.
 * A Bug's Life: Francis is a male ladybug who doesn't take kindly to people assuming all ladybugs are female. The fact that his name is gender-neutral doesn't help.
 * In Aladdin, Iago really didn't like playing the part of the dumb animal for one particular reason. "Polly want a cracker?"