The entire plot of One Piece seems to be based around this. If you fight Luffy without having hurt one of his friends, you at least have the possibility of victory. If you hurt one of his group... not so much.
And if you hurt one of YOUR group members, you are so screwed. Boa Hancock & sisters, we're looking at you.
Also, let's not forget Captain Kuro, whom Luffy defeated in righteous anger for turning on his own crew.
And Caesar Clown, who gleefully sacrifices his own Mooks for the sake of his experiments. He got constantly punched to the face and finished with an Armament-haki giant Bazooka for his trouble.
Don't forget about Arlong, whose made Nami cry after not only killing her mother years before, but also made it so EIGHT YEARS of work was all for nothing! The result is Luffy throwing a huge sea monster, and delivering a brutal beatdown to Arlong
Never hurt people who shown hospitality to you. He won't hesitate to try and kill you, even if you're his own crewmate. If only he gave Zoro the opportunity to explain why he fought the people of Whiskey Peak...
Do NOT say you're the one who is gonna be Pirate King within Luffy's earshot. (Not as mockery. He at least tolerates the ones he sees as rivals)
As of the timeskip, he's also not terribly thrilled with people who harm big brothers
And somehow, Hody Jones thought it was a good idea to threaten Luffy's friends, threaten the Kraken's younger brothers, and claim to be pirate king. He's lucky Luffy just gave him a royal ass kicking.
While played more for comedy, taking his meat is a fine way to piss him off.
A new way to piss him off is to mock his brother Ace's murder. So long, Don Chinjao.
Zoro is normally the type of guy who doesn't take revenge on things. But once, Ohm's traps brutally cut and mangled Chopper...
He destroyed Kaku after being at best evenly matched throughout their fight after Kaku called their efforts useless (though in the manga, Kaku said nothing). "Don't get too carried away."
Much earlier, it becomes clear that he doesn't take kindly to being accused of being unable to keep a promise. Due to the fact that his life's ambition is pretty much built off of a promise that he made to Kuina, this is understandable.
Do not spend money without consulting Nami first. Do not steal anything from her, especially if she stole it first. The repercussions for those two can be comical…but above all else, do not hurt the people she cares about. Miss Doublefinger, Kalifa, and Absalom are among those who wound up electrocuted as a result of doing this.
Usopp is a Lovable Coward, and would rather run away than fight. But if you insult Luffy in front of him, you're doomed; he may be the weakest of the Straw Hats, but he's still a One-Man Army when he needs to be, and he won't put up with insults to his captain. Mr. 4 and Miss Merry Christmas found this out the hard way, after hitting him with enough force to kill a normal human a thousand times over.
Sanji's biggest berserk button is when anyone wastes food, including using food to fight with. He and Old Man Zeff almost died of starvation when Sanji was a child, so this one's very understandable.
A close second is if anyone mistreats a woman, especially Nami, Vivi, or Robin.
A third is his wanted poster. Don't bring it up, but if you do, do not say it looks like him.
Chopper will beat the hell out of you if you take the concept of life lightly. He also lost his shit when he found out that Caesar Clown was experimenting on children and kept them in captivity with drugs.
Robin is also quite angered by those who disrespect history, as she demonstrates on Yama in the Skypiea arc. She also gets angry when people talk about her past and why she got her bounty often because what they're saying is not true.
For Franky: do not hurt his Family. Do not insult his master/foster father Tom. And do not take his speedo.
Brook's afro is precious to him as it is the last defining feature he has that his old friend Laboon can recognize him by. So... Do. Not. TOUCH. THE. AFRO.
As of chapter 645, Brook hates people who waste lives. And considering his past, this is understandable.
In One Piece Film: Strong World when man-eating ants ignore Brook because he was considered "leftovers", he angrily states it was "a bit inconsiderate" and proceeds to cut all the ants down. This Berserk Button is pushed again in Chapter 682, when the little dragon from Punk Hazard looked disappointed that Brook didn't have any meat on his bones. This actually serves as a minor plot point, as it reveals that Kinemon also hates dragons, but for a much darker reason.
Also, Buggy the Clown. If you insult his clown nose, he will freak out, and given the chance, he will shoot you with a cannonball capable of destroying several city blocks. When you account for the fact that he tends to mishear things and assume they were insults to his nose...
Recently, we get one for Boa Hancock: You so much as lay a hand on Luffy, and not even a Logia Devil Fruit Power will save you from the Snake Princess tearing your ass to shreds. Yeah, when Sengoku mentioned that Hancock is strong? That is NO Informed Ability, she's the strongest Action Girl in the whole world.
If you so much as injure any of Shanks' friends (such as Luffy), expect Shanks to show no mercy.
Portgas D. Ace can be seen as a deconstruction of this trope because in the Marineford arc, when he was rescued from execution, he let his emotions get the better of him. When Akainu starts to insult Whitebeard, Ace is drawn into a hopeless battle that ultimately kills him. This happened despite everyone, including Whitebeard, warning him to run away.
If anybody mocked Eustass "Captain" Kid's dreams about becoming the pirate king, he wouldn't hesitate to straight out kill them for that.
Smoker cares deeply about his subordinates, even if he doesn't show it. Just try and lay a hand on them. Vergo, we're lookin' at you.
Bartolomeo, a character who first appeared in the Dressrosa arc, was introduced as a rude, Ax-CrazyJerkass. It's bad enough if you provoke him at all, but he absolutely worships Luffy; say one bad word against him in this fanboy's hearing, and it will be the last thing you ever say.
Out of all people, Trafalgar Law's berserk button seems to be a massive one. If anyone insults, laughs at, or slights Donquixote Rocinante, a.k.a. Corazon, he noticeably loses his cool and flies into a violent, screaming fit. And God forbid if you actually kill him. After Doflamingo murdered Corazon, Law vowed to murder Doflamingo at all costs, which is the very explanation as to why he's perfectly happy to sacrifice his life in a Roaring Rampage of Revenge in order to avenge his most cherished person.
Donquixote Doflamingo has two notable ones: people who would mock or insult his family in any way, and people who bear the name of D.
One of Doflamingo's top three executives, Pica, also has one: do not mock, insult, or laugh at his voice. And unfortunately, in spite of—no, because of the fact that he is a very tall, very muscular, and very powerful human, this button is pressed too often thanks to how little his high-pitched voice suits him. Heck, even Zoro was incapable of holding back his laughter.