/em discodance
My single most memorable moment in the game came a few days after seeing someone appear during the cutscene in the LGTF where the Clockwork King appears, they got stuck in the background and no one in my normal gaming group knew that would happen.
So, a few days later we have someone running the NPC to the door to trigger the cutscene, everyone else fighting the ambuses, and the runner is about to Team Teleport everyone to kill the Clockwork King. Standard practice. Except I decided to sneak off, going dead silent in Skype, and stand where the King is going to spawn, center as best as I could from memory, and do /em discodance. Everyone died. With laughter, though some did die in game because they just completely stopped fighting they were laughing so hard.
I would never claim to be the first to do this, because I seriously doubt it, but I was the first any of our group ever saw, or the PUGs we had, and it became pretty popular not long after.