?

Me: Ryan, don't hit your sister's bottom
Ryan: Okay, I'll Booty Knock
Me: ???!!
**Booty Knocking - 2 people bonk booty's. Or 1 person walks their booty into another's

Either way, it's been classified as a new fun game.  This might also be known as a 'bee sting' if you get some momentum going and can knock the other person over.