Bum Knee 

When your knee is injured and you remember the times before the injury.

Most Common:

I would have made pro if it wasn't for my bum knee.

Bum Knee by wordzilla March 14, 2011

bumknee 

The act of sliding one's penis in between the back of a bent, sweaty, knee.

This bitch gave me the craziest bumknee after her workout...Amazing!

bumknee by Chris "Backstreet" Massaroni April 29, 2011