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1.
to put peanut butter on your knuckle, insert it into a woman's anus, lick it out with your tongue and put it back in the peanut butter container.

Also known as: p-b poop, the washington carver anus lick, the tasty sunrise, the sloppy sunset, gas sandwich, penis butter sunday, the lippy skippy tongue tongue, ghetto moutnwash, sloppy cosby.
Example 1: Sam, instead of a hamster for Christmas, I'd like you to give me a sloppy knuckle.

Example 2: Mom, I think Dad left a sloopy knuckle in the peanut butter again.
by The Real Tay-tay November 05, 2010
 
2.
origin and meaning unknown.... one can only guess
After I punched the clown the other night, I had a horrible case of sloppy-knuckles
by hewchardon May 22, 2003