LEEEEROY JEEEENKINS!

 

Leeroy Jenkins first originated in World of Warcraft. In this video, some friends are about to enter a dungeon, and are planning their strategy. Now one of their friends are afk, and at around 1:25, he randomly comes back, shouts "LEEEROY JENKINS" and runs in to the dungeon. So at this point all his friends realize what just happened, and the whole mission just collapsed. If you want a better explanation, look at the video below. It even has a card in Hearthstone, one of my favorite games.