Forearm grease 

(noun)
Phenomenon that occurs when wearing a long-sleeved shirt, jacket, sweater, etc. while carrying out a messy task with the hands (such as painting, eating tacos, sorting garbage, moving dusty furniture, changing a diaper, unclogging a toilet, or having sex).

The sleeves are rolled up in order to aid in providing more freedom and mobility with the hands, however, those gotdamn sleeves keep falling down and refuse to stay rolled up, resulting in them getting in the way and being dirtied in the process.

Usually and inexplicably happens with a piece of clothing that the owner particularly likes.

Larry: Yo, what's all that crud on the sleeves of your varsity jacket?

George: It sucks man, I was wearing it last night while Simone and I were doing the nasty. We were so hasty that I didn't feel like taking it off, so I rolled up my sleeves and proceeded to zoom-zoom in her boom-boom! ....Unfortunately, stupid gravity kept making the sleeves fall down and I got sex juice all over them.

Larry: Damn, son. Bad case of forearm grease. So.... how's dat Simone ass?

George: Larry, stfu

Forearm grease by Mr. Berzerker January 1, 2014