To be hurt, rejected, or any other type of inconvenience. Not to be confused with the literal form of "sat on" in which someone literally sits on you.
Guy #1: Dude, you totally just got sat on by that Koopa Troopa!
Guy #2: I know! I was THIS close to getting to the end with Bowser and that demon turtle just came in like "*whachow* I'm not just a turtle anymore, I'm a TEENAGE MUTANT NINJA TURTLE that's gonna whoop your little ass!"