This guy in a video clip of a game called world of warcraft or WOW who is completely nullheaded. Basically this party, or group of people in an rpg video game, were taking their time strategizing how to take on this group of "monsters". Suddenly Leeroy stands up in the middle of the elader's sentence and yells, "OK CHUMS, LETS DO THIS; LEEEEEERRRRROOOOY nnJJENNNKIIINGSS" The group frantically trys to save leeroy and execute their plan but fails.
Now people refer to "unsmart" aggressive playing as leeroying or with something assosiated with leeroy, the rp legend can be seen at
Ok guys, nobody aggro this monsters. If your a fucking leeroy ill hack into your computer you stupid fucking nubcake