rump grease

An oily, malodorous substance found in the folds and cracks of one's butt. Typically found after a hasty wipe and/or following a rigorous workout routine. Similar to butt cheese or duck butter. Could also be a prime ingredient in the making of truffle butter.

Noun: I itched my butt and retrieved a healthy dollop of Rump Grease.

Verb: My girlfriend Rump Greased my driveshaft. I had to take an immediate shower. It itched for a week.