Shit Knees
The red marks that develop above your knees which are caused by your elbows resting on your legs while taking a dump for a prolonged period of time.
Dave is watching a movie waiting for his girlfriend Sally to return from the washroom.

She returns wearing her regular outfit which includes short shorts and a tank top, but something has changed.

Dave: What the fuck is that?

Sally: What?

Dave: Your big red santa fucking rudolph fucking koolaid knee parts.

Sally: Oh, you mean my Shit Knees?

Dave: Eheheheee... Get yo smelly ass underneath these covers..

*Disclaimer* Dave is black
*Disclaimer* Black people cannot develop Shit Knees