In "Chrysalis," the Queen manages to break Zachary by torturing his Rangers in front of him, making him think he witnessed Niko's execution, casually discussing her plans for Earth in front of him, and following it up with telepathic Mind Rape. When Niko actually comes back with the BETA fleet, the Queen, in a rage, starts to kill her in front of Zach. He flips out, grabs the Queen, puts them BOTH in the Psychocrypt, activates his bionics without having access to his badge and blasts her into ash.
"If it will end the nightmare, then I don't care. I'm already dead. This is for the two years of my life you've stolen from me, you BITCH!!!"
In Chong Sheng, Katara goes on one of these when the Rough Rhinos taunt her after torturing and murdering Jet right in front of her. Though it warrants mentioning that the distinct lack of roaring on her part is what makes it Nightmare Fuel.
In the 'Help Me, Dr. Hazama!' fanfic 'Disaster-Piece Theatre', we have Kokenoe inexplicably growing to gigantic sizes and taking out almost the entire cast because they helped replace her favorite game
In Twisted Colors, this is Gadvein's...whole reason for existing: killing the fuck out of everyone who ever supported Britannia in the EU, or anyone who supported Kyrl, or anyone who supports anyone who supports Britannia...he has a humongous list of people he wants dead, and he is not stopping until every single one is dead.
The Stars Will Aid Their Escape: When Trixie (who the heroes have been tricked into believing is the Big Bad) appears at Canterlot during the eclipse celebration, Applejack goes into a blind fury and attacks her for what happened to Apple Bloom. She very nearly beats her to death before Rainbow Dash talks her down.
Applejack again in My Little Castlevania, during the climax of the first book. When she finds out that Marble raised her parents as zombies during the attack on Ponyville, she goes into a blind rage and nearly hunts Marble down to kill her — fortunately, Big Macintosh talks her down, reminding her that due to Marble's Evil Plan, any harm done to her will mean the deaths of all the foals she poisoned.
In "Blind Mans Bluff", Nick comes extremely close to exacting one of these on Brenda and the rest of the Angels when Brendagloats about one of her teammates torturing Ellis to death. His Berserk Button was smashed to the point of no return, and he was in such a frothing rage that he was planning to kill all of them with nothing but his bare hands, even though they were heavily armed.
In A Growing Affection, after the Blood Drinker Doraku appears to kill Hinata in chapter 11, Naruto unleashes two previously unseen jutsu, and shreds large chunks of the demon's body with Rasengans. When the demon taunts him with the fact that Naruto can't kill him, Naruto blows a hole through Doruka's chest, drives a stalagmite through the hole, pinning Doraku to a cave wall and then has his Blood Clones collapse the cave on top of the "vampire".
Whilst not stated in the actual series itself, Waltz of Third Fang's "Yet Again" went on one so terrible that it not only gave him the names The Red Flood and The Eyes of Stone. And it messed him up, to the point that anyone stupid enough to remind him of that day better pray that they're corpses are still recognisable as human once he's done.
Spock in Atlas basically orders one of these when he feels his lover Jim Kirk killed through the mating bond they share. It results in probably one of the coolest lines ever to be delivered by a vengeful Vulcan; "Find her. Prevent her goals. Destroy her plans. Break her dog. Lay waste to all who gather around her. Ensure that she comes to regret ever hearing the name James Tiberius Kirk." This is eventually carried out in a Crowning Moment of Awesome.
Abused daughter Batel of Toy Hammer's roaring part of her rampage of revenge begins when she calls out her step-father, while giving in to her more evil nature. Not much detail on what exactly, but the sadistic man treated the mother and daughter both like 'toys', so the worst can be assumed.
Her revenge started earlier with a very ill-advised pact with the Chaotic Evil Chaos Gods.