#1) a confident swagger you bring out when you are about to get ready to tackle something difficult, or when you are about to take on a challenge. Or when you are getting ready to get down to hard business.
#2) When you are ready and pumped up to party really hard.
Person1: "Tomorrow's your job interview, right? Are you ready?"
Person2: "Yea son, I'm bringin' out my GAME FACE."
Person1: "You're turning 21 tomorrow. Time to hit the bars and black out, so be ready to bring out your GAME FACE."