Used in video games during situations where one team either has been or is being utterly raped
by an opposing team. This lets them know that you find their performance disappointing and that they should increase both their ability and performance. While the intent behind saying it is to encourage them to play better, this usually has the opposite effect if they are unable to do so and sometimes results in a phenomena known as the ragequit
Team 1: "Shit, we're getting steamrolled here..."
Team 2: "STEP YO GAME UP!!!"
Team 1: "Fuck this shit, i'm leaving."
Team 1 disconnects from server.