'Slap My Elbow' parodies silly rap songs telling you to do something....

For example... there was a song "back in tha day" that said over and over again..

"Lean back! Lean back!" and everyone "leaned back" to the beat.

It is parodying repetitive hip hop that tells you to do a simple body movement over and over again like some sort of ghettofied instructional dance video.