The ridiculous expression on one's face after consuming copious amounts of alcohol and/or drugs (namely cocaine). Another variation is "the face of guy." Also used to describe someone who has spent the night at a "face party"
Dude: Did you see Toby last night? He was so fucked up! He had his guyface on fo' sheezy.
Guy: I was rockin' out at Dude's face party last night, and I left with the face of guy.