The remains after brutally owning someone, whether it be on a video game, i.e. Halo 2; or in real life. It tends to be found in a person's mouth, or around their genitals. The saying of this expression usually follows the phrases "Get Raped" or "Eat that shit bitch".
Dave: STUCK! GET OWNED BITCH!
Noob: Ewww what is this stuff?
Dave: Rape sauce, sucka! And you just got smothered in it.
Kid 1: Aw man, i just stepped on a piece of gum.
Kid 2: Not only that, but you got rape sauce all over ur new sneakers! Sucks for u!
Kid 1: Darn it!