A reference to the character in Left for Dead 2, who usually has an expressionless face. If someone would have no expression on their face they would be "coach faced".
Man: "My girlfriend had a Coach Face during sex last night, apparently my dong is too small".
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?"