A play on the term "in your face motherfucker!"
A facial refers to something throw back at someone in an embarassing manner.
A variation is "you just got faced!" or simply "face".
Commonly used in the Torrington CT area in the late 80's and accompanied by putting an open hand over your own or the others person's face.
"Hey dude, you thought your car was the fastest but I just smoked your ass!!!! Facial!!!!