When someone is undoubtedly overly intoxicated, typically resulting in that person passing out, ending their night.
Person 1: "Where's Mitch?"
Person 2: "He smoked all his weed and drank all his alcohol and is now passed out on the couch."
Person1: "Oh shit...yeah, he's done for."
It means that someone is or will be in trouble.
If i don't get my papers on time i'm done for.