Dragon Ball Multiverse: As implied by the title, Zangya is on the receiving side on one from Son Bra. All it took was one air pressure attack, and Zangya was already dead.
In El Goonish Shive, the Big Bad is invincible... until he makes Grace angry, at which point she proceeds to kick his butt without much trouble at all.
In Funny Farm, ASCII goes into one when his slot machine "girlfriend" gets shot. He accompanies his rampage by saying leet versions of "delete", "format", and "defragment".
Girl Genius has this for its Sparks. When they get in the Mad Place, they unleash all their most devastating gadgetry and can throw around clanks single-handedly. However, it is said that this is also the reason for most lower level sparks' deaths. They get in a rage without the ability or sense to keep themselves from dying.
Tarvek flies into one of these while fighting Zola, beating her to the point where she tries to surrender — only Tarvek isn't listening to silly notions like that.
Agatha goes full tiltafter Lars is killed. Thank goodness for Sparky pies.
Complains Of Names from Goblins, a barbarian, after Chief's torture and death at the hands of Kore. Kore ticked off the bull and now he's getting the horns!
Aradia Megido is first introduced as a depressinglyEmotionless Girlbecause she's a ghost, but later on when she gains a new robot body she becomes capable of showing one in particular. Rage.
Karkat Vantas walks around in a state of perpetual ire and will verbally tear into anyone with little provocation, so it's kind of a subversion that he doesn't do this.
Gamzee Makara's title is the Bard of Rage. From all accounts, it manifests as him being nigh-unstoppable when he gets going — he is said to have dealt the most damage to the Black King with just one strike, and that was when he was high. Whenhe'ssober, this trope is more or less his default state. To wit: what he did to Nepeta...Eventually however, Gamzee's rage is stopped by Karkat via a Cooldown Hug.
Rose enters one after learning that Bec Noir had killed her mother. Seeking revenge, she well and truly loses it when he kills John at the very beginning of the battle, prompting her to destroy a large percentage of the battlefield in an attempt to kill Bec Noir. This being Homestuck, Rose's attempt is in vain and she eventually gets killed (and to add to insult, she did no damage to Bec Noir.)
Bec Noir goes into this after Jade dies again, and slaughters most of the Trolls' Dream Selves in their session.
John Egbert, despite his usual calm personality, got into this state twice:
After he was already enraged by Davesprite being more of a jerk than usual, he meets Jack Noir and proceeds to beat him so furiously that he's unable to fight back. Jack has to bind John with tentacles just to get a chance to hit back, and even that didn't work. In one hit, John manages to harm Jack nearly as much as Rose through the entire fight and cause tremendous damage to his reputation in PM's eyes..
On his second meeting with Caliborn, he unleashes all the hatred he built up from their previous encounter. At first, Caliborn puts up a good fight, but soon enough ends up on the floor, receiving one punch to the face after another. The only thing that stops John is his abrupt teleportation out of the fight, by which point Caliborn is lying on the ground, looking borderline traumatized.
After Slick breaks the God Tier clock, Doc Scratch finally gets fed up with his behavior, and proceeds to beat him into a pulp (with a "teach yourself programming" book, no less) and punch him through the wall, sending him falling several stories to the ground.
In Hookie Dookie Panic, Adda pulls a few of these, the biggest being when she loses a Dance Dance Revolution tournament due to a fight going on, and she proceeds to go into a psychotic rampage and kill those responsible for the fight.
Dr. Jean Poule in The Inexplicable Adventures of Bob! can go from adorable Girl Next Door innocence to blind fury without too much trouble. This rarely manifests as physical violence, as the mere force of her yelling is usually enough to produce results (i.e., Bob: "Wow! Thanks, Jean! You're swell at yelling at people!" Jean: "Well, the secret is to enjoy it...") but it has gotten her into fights upon occasion.
In Sam & Fuzzy, Mr. Blank has his moment of Unstoppable Rage against Mr. Black, at least in the beginning. The funny (or creepy) thing is, the audience could already sense the doom months ago.
Tessa in chapter 2 of Sleepless Domain, burning out all her magical power in the process.
In Slightly Damned, Buwaro was born with permanent Unstoppable Rage. The only reason he's so happy-go-lucky is because his star pendant keeps the rage in check.
Averted in Sluggy Freelance. Torg appears to go into one of these after Horribus kills Alt-Zoe, but, in a rare moment of rationality, he realizes saving the world is more important than a grudge match, and runs away instead.
Upon finding his best friend Alex beaten to a pulp by Forrest, Ben's eyes go completely white and he pummels Forrest so viciously that it's described as an assault rather than a fight. It's only Alex regaining consciousness and telling him to stop that brings Ben back to his senses.
History repeats itself after Naksung attacks the already-beaten Ben with a wooden beam. Alex intervenes, beating Naksung in a fury, only for Naksung to grab the broken beam and retaliate. Ben, at that point thought unconscious, gets back on his feet, downs every one of Naksung's Mooks with a single blow, and then starts laying into Naksung so badly that the others are certain Naksung will die. With Alex unconscious, Jake stops Ben's rage instead by stepping in front of Naksung, knocking Ben out of his one-track bloodlust.
We Live In An MMO?! has Rando, who when his Berserk Button is pushed one-too-many times unleashes a terrifyinglybrutalbeatdown on a trio of other players. Unlike many examples this isn't treated as a Moment of Awesome, as it leads to the deaths of those three players and Rando being sentenced to a Perma-Ban by the world's Guards.