entry so please be nice.
The Villain has done it. He pushed the wrong button. He revealed the wrong secret. He threatened the family member one time too many. Now the Hero is very angry. Good, its always nice to tease the...wait a minute? Did the Hero just rip that Mook's throat out?!
Power Limiter? Removed. Superpowered Evil Side? Engaged. Thou Shalt Not Kill? Recended.
Congratulations, Villain! You just pissed of the Hero. You're so dead.
Examples (SPOILERS): Superman in Superman vs. The Elite when he fights the Anti-Heroes by fighting exactly like they do. Miss Martian in Young Justice when Psymon threatened to reveal her secret of being a White Martian to her friends. Batman in the Hush storyline when he is this close from killing Joker when he killed his friend. Sisko in Star Trek: Deep Space Nine when he destroys a planet's ecosystem to catch a traitor. The main character in Shooter when he kills the bad guys when they couldn't be charged for framing him for attempting to kill the president and for kidnapping (and possibly raping) his dead partner's widow.
Possibly belongs in Super Trope "You Wouldn't Like Me When I'm Angry"
Differs from Unstopable Rage because while the Hero is obviously angry, he is still bound by being a hero. He may be angry hero, but he is still a hero. He may stop holding back, but in the end he won't kill the villain.
Differs from Berserk Button because that is just one action that causes an severe angry outburst. This trope is when a hero is so pissed off that he stops fighting like the Hero.
Differs from Beware the Nice Ones because some heroes are not nice (see Batman, Wolverine, et. al.).