Thank you Urban Dictionary

[hugin_munnin]

1. knee-breaker

Taking a leak while sporting morning wood. To keep from spraying the wall, you lean forward as much as possible with your legs straight, to the point where you think your knees are gonna snap.

Example:
I had to take a serious knee-breaker when i woke up this morning!

Comments

[game_whino]

You lean foward? I usually either do a hand stand or stand back and work out the trajectory...I'm going to have to give your way a try

[illusionjunkie]

I always called it the superman manuever...

[grono]

Example:
I had such a knee breaker that I had to pee in the bathtub.