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2.
The second knuckle in (heading towards the hand). Originating from the knuckle at which you stop at when inserting a digit into another's asshole.
Used to warm up/stretch out an asshole before anal sex.
I was playing ping-pong and the ball hit off my poop-knuckle.
by DMazzIV August 22, 2006
 
1.
The result of an improper angle of approach when wiping your ass from a particularly messy poop-session. Poop gets on your knuckle. Usually occurs when you lift a cheek to the side and attempt a wipe.
Steve liked to lean to the left when he wiped his ass. This often resulted in a nasty case of poop knuckle.
by Bspot January 08, 2008
 
3.
When wiping the ass after an exceptionally productive poop, a knuckle is accidentally raked across the large, volcanic cone-shaped pile.
I must remember to give myself a courtesy flush to keep from getting these damned poop knuckles.
by padabo October 02, 2011
 
4.
A place on a poop where it is thicker than elsewhere on the poop.
Sorry I took so long in the can; I got stuck on a poop knuckle and it took a while to force it out.
by skullfragment August 21, 2008
 
5.
The point to which poop comes up the shaft of the penis after having anal sex with someone who didnt "clear themselves" before hand.
Damnit carl, you forgot again?! This poop knuckle has to be at least four inches...this time your cleaning it.
by BGSC March 03, 2009