I'm sure we've done some crazy stuff, but I can't remember too much of it. Let's see...
There was the Deck of Many Things abuse, which lead to the entire party turning evil, the Dwarf barbarian changing sex, and drawing the "you die" card 3 times, using up my 2 wishes, and forcing us to bargin with a... something... to reverse the effects of the cards. We never made it to the end of the dungeon. Well, we did, but we were wounded, out of healing spells, and about to fight a green dragon. We didn't continue...
There was a GURPS game based on Skyrim, but without magic, and our characters could barely use their shouts in public without being hunted down. Anyway, one of the PCs was meditating in his room, because he took some kind of "short temper" flaw which I can barely remember anything about, and the other PC, probably secretly a worshipper of Loki, went to a nearby farm, bought a pig, walked to the meditating guys window with it, and made enough strength rolls to eventually lift up the pig, and throw it through the window at the guy. He was reduced to 1 HP and suffered a major wound. The game didn't last much longer...
And there was a Golden Heroes game (Squadron UK, I think it's called now), where we had to rescue an American superhero, and my new character joined the game. A psychic, cybernetic alien, who turned the enemies guns into sticks. We beat the nameless NPC hired goons, and broke into a submarine. We called in the Americans, and for reasons now lost, the alien punched the commander-y guy hard enough in the face to render him comatose. The rest of the guys gunned the alien down. The other heroes were arrested and now America hates our group, just like the rest of the world...
I'm sure there's more, but I can't remember any of it right now. It's almost 6 am and I haven't slept yet...
Edit: Oh, there was a Savage Worlds campaign based on... some book that the GM had read. Anyway, we were supposed to be... I can't even remember. But I founda blacksmith where I could get a chestplate (I had plate arms, plate legs, and a plate helm, and no chestplate...), and found an elderly man, who gave me a bit of paper to come back to the shop with. After enough time had passed, I returned and gained a suit of armour where the only visible openings were the eye-holes. Upon exiting, the shop, and the backsmith, had vanished. Later, while exploring a dungeon, I fall down a trap-door and end up in a fancy tomb, which held a talking sword, which wanted me to take it. Turns out it was an elf king who wanted to kill the gods, and I was happy to turn on my party and help it, and by the time we stopped playing, I was a 7-foot-tall walking tank. And we convinced the "medicinal herb"-smoking Gnome to join us, with the promise of 4 extra feet of height, god-like power, a physical manifestation for one of the hallucinogenic side-effects of the "herbs", and a Bag of Holding full of cookies.
And there was a Paranoia game that started with a cinema that spouted "Communist Propaganda", in the form of some old Chuck Norris films, and ended with a battle against a giant, radioactive, super-powered Chuck Norris. It's a good thing I had a psychic mind rape ability that everyone now knows about...