I term meaning "You are fucked" or "There's no way out". Often applied to non-severe issues such as a flat bike tire. However, it can also be used to taunt a friend when they encounter an legitimate reason to worry.
Another use implies threat.
Use 1
Person 1: "Dude, that ugly girl asked me out and I was so drunk I said yes!"
Person 2: "You're done son."
Use 2
Person 1 spills hot coffee all over some douche bag at the food court.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"