It's some kind of MMO game, the video is freakin hilarious. It starts off slow, they even calculate their survival percentage. Then, all of a sudden, Leroy belts out his battle cry and starts kicking ass.
Then all the nerds get pissed.
http://www.shagwall.com/leeroy.wmv
LEeeeeeeeeeeeerrrrrooooooooyyyyyyyyyyyyy!
It had me laughing my ass off!