He'd find a few of those empty cardboard boxes that are frequently found in the game, open them up, tape them together and place them on the floor. He'd look around, make sure the coast was clear, and start break dancing while taunting an invisible enemy with his skills and some old-fashioned trash talk.
"Oh snap! Uh huh, yeah, and what? Yeah, oh ****, I'm too good. You can't touch me bish! Uh, uh, uh, yeah, that's right. What now? What? Whoa, you talking to me? Oh no he didn't. How about some of THIS, and some of THIS, and THIS and THIS? Oh, give up? *****ass mofo."
That's how Gordon Freeman rolls.