1. A face made during the uncomfortable discovery that you have gas or the face one makes during or after the release of said gas by someone else.
2. The look you give someone when they are saying or doing something you think is dumb as hell.
Dude 1: Shit! I dropped my gum on the ground right next to that pile of dog shit and vomit. *Bends down to pick it up*
Dude 2: What the hell are you doing?!?!?
Dude 1: It's my last piece! It didn't pass the three second rule...I'm chewin' it!!"
Dude 2: *gives Dude 1 the 'gas face'*