Halo: A certain mod released by a gamer is "Who's Laughing Now?!" a variation of Gruntpocalypse where the grunts are made four times tougher, immune to headshots, and benefit from two skulls which generate both extreme accuracy and bullet spam.
Pac-Man. The game is founded upon the ability to change the game from fleeing indestructible enemies to eating them.
Mr. Burns: Ha ha! The hunter has become the hunted!
Heroic (kinda) example: Tombstone from Freedom Force uses this sentence when he's returned from the dead and confronts his wife's killer, who had framed him for the murder and sent him to the electric chair.
Tombstone:You. The innocent die while the guilty laugh. Who's laughing now?
Lotte Carmine was a scientist working at Sector Seven; for the entire time he did, he was ignored by Kokonoe, mocked by Relius, and eventually broke up with his love. He got his revenge, though at terrible prices. Then again... Eating people, insect powers, being able to deal a lot of damage... maybe him turning into Arakune isn't so bad. This is, however, subverted that the people he ate was relatively minor ones, he cannot consume his true target that is the Azure within Ragna the Bloodedge. He spends his time getting beaten up by nearly everyone (and ends up easily captured by Relius), other people (including Kokonoe and Relius) talking on how he's still a failure at his form (and they're actually proven right and Terumi hammers it down to him), his speech got impeded so bad that he can't get everything across clearly... He certainly wished to invoke the trope, but utterly fails in the middle, as he ends up with even more ridicules than respect.
Then Chronophantasma proceeds to reconstruct it. Turns out, Relius capturing him comes with the package of modifying him, giving him a boost of badass AND coherency in speech. Then he got 'Observed' by Hazama as Arakune, not Lotte Carmine, therefore he gets to keep his more powerful blob form forever. How badass? Let's just say he goes from everyone's punching bag into capable of beating the crap out of Bang Shishigami and stole his Rettenjou, AND fighting Hakumen and surviving instead of getting cut down. Yikes.
Admit it, you've laughed when you ended a poor mook's existence with the Vanguard Rush from Mass Effect 2. And you've also probably got a good giggle realizing you're the only one who can do it. And then "Lair of the Shadow Broker" rolled around, and you met Tela Vasir. Not so much funny as just fun.
In RuneScape, both Lucien and Bilrach were both looked down upon by both humans and their own kind, and were disregarded as frail and weak. Now Lucien is on his way to godhood, and Bilrach is the leader of a massive army of demons, Eldritch Abominations, and powerful warriors.
In Portal 2, after Wheatley gets plugged into GLaDOS's body. He directs this attitude towards Glados, who had spent a few seconds calling him an idiot, and you, who had made all this possible for him in the first place and been with him every step of the way; he claims you've been bossing him around constantly when the opposite is true.
In The Legend of Zelda, the notorious Cucco calls on its comrades after being whacked with a sword one too many times by the hero, Link.
In Winter Shard, the game opens with a lonely, desperate Frederic being continually denied food and shelter by the people he tries to seek help from and then having his right arm ripped off by Temonz, for the sole crime of being the son of a man accused of treason. Naturally, when he's resurrected and granted dark powers by Krotus, he exults in getting his sweet revenge on these people.
A heroic/player version is possible in Batman: Arkham City. As the game progresses — and in the harder levels of Challenge Maps — you'll run into stun-baton-wielding mooks, and they take great pleasure in destroying your combos, shaking your screen, giving their buddies ample time to take a chunk off of your health, and generally being one of the most irritating form of mooks in the game. One of Batman's takedown moves involves him taking the stun baton out of the mooks hand and shocking him with it.
Lollipop Chainsaw: The Big Bad's whole motivation for bringing about a Zombie Apocalypse. To get back at everyone in his high school who ever made fun of him or humiliated him- including the game's protagonist, Juliet.
Baldur's Gate II: Shadows of Amn: This is the offscreen backstory for Kalah the illusionist, who somehow gains great power and turns the circus where the worked into a Bigger on the Inside fantasy world where things are not as they seem, in order to take revenge on those who made fun of him — basically making a Power Fantasy real.
The premise of Days of Monsters is that your character was bullied as a kid and turned to mad science in order to get revenge.
Anytime in Dawn of War: Dark Crusade, when the Imperial Guard manages to deploy a Baneblade. IG is a Redshirt Army, whose viable tactis boil down to "have more soldiers than the enemy has bullets" and the Baneblade is a huge investment in time and resources. However, the eleven-cannoned behemoth is nearly capable of clearing maps on its own, and when it rolls out... to quote the game:
In Ace Combat X, one particular mission forces your Ace Pilot to drop unstable and prone to accidentally detonating and killing you antidote-bombs on nerve gas outlets. Your flying is severely limited during this due to the instability of the bombs, and the enemy pilots chasing you relentlessly ridicule you for it. Once you finish stopping the gas attack, the bombs magically empty out, and you are free to run the enemy pilots through like any other, and they suitably shit their pants when they see you for the Ace Pilot you REALLY are.