A "monkeys paw" is when you're taking a shower and you're out of wash cloths Once you get to washing your ass, you soap up your hand and get down there to clean it all out with that soapy bare hand. You're then left with a clean ass but in return, no matter how much you clean that hand, it feels dirty for the rest of the day.
I cant eat tacostoday, I gave myself a Monkey's paw this morning and I forgot which hand it was.
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).