Slappin' de bass
the act of stimulating a female reproductive organ by the manual use of your hand and/fingers as a stimulus. The action can be termed simply as fingering, but if you look closely it actually looks just like somebody rocking out to a sick air bass solo.
On the night of prom, me and my smokin' hawt date decided to ditch the dance and I videotaped twenty minutes of her slappin' de bass. Then we screwed. Best night of my life.