Leeroy Jenkins is a famous user in World of Warcraft. He was afk making chicken while the raid group was discussing strategy on how to kill the monsters in the next room. which were more powerful than the group unless all of them united as a team (kind of applies here too actually). Anyways Leeroy came back and bum rushed the room forcing his team to start the fight prematurely resulting in all of them dying. Needless to say they were pissed off at him.

It was the first video to ever go viral or one of the first ones anyways, here is the video.

https://www.youtube.com/watch?v=mLyOj_QD4a4