to smack the person,in the head, who is giving you a blowjob or head. Also, it can be refering to the song by the trance artist, Alpha Twins.
a girl is giving a guy derb, a blowjob, and the guy slaps her or hits her in the head while she still gives him a bj. which that is smack my derb.
by Kr0nIc SkR3aMz October 24, 2010