Happy belated birthday.
While playing pick-up with a guild in WoW I learned one member had been to Naxxramas in the original version, which was probably the most difficult raid the game ever had. He was an officer with his guild at that time and the officers came up with a prank to play on their raiders.
In the first room of the raid is a siamese cat named "Mr. Bigglesworth" who, if killed, causes the end boss to shout death threats. The officers started a rumor that if they could defeat the final boss without ever killing the cat then they would get him as a pet. The raiders loved this idea and made sure to not use any damaging spells nearby - one hit would kill Mr. Bigglesworth. Whenever they were getting ready for the final boss one of the officers would sneak off and kill the cat, triggering the boss and the raiders to start shouting.
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Another story I read about was a guy who, for one reason or another, asked his friend to look after his Alliance character while on a trip. Said guy logged on after his trip to find a few problems:
1.) His character was completely drunk.
2.) His (male) characters was wearing only a white wedding dress.
3.) Every slot in his bags was filled with stacks of booze.
4.) He was in the middle of a Horde city.