The act of someone slapping, swatting, or smacking another someone on the butt as they walk by as a way to tag, mark or provide admiration to the one receiving the smacks’ body.
Girl walks by; guy slaps her on the butt.
Girl 1: Ouch!
Girl 2: Dang girl you just got a Bootytag!
When you are getting a blow job and you reach over her back and fingerbang her from over the top, coming in from behind. You must use the butt crack to cradle your wrist and/or forearm.