The act of masturbating with sandpaper. The grit is not important, but usually the lower the more hardcore you are.
Guy 1 - Dude I went to menards last night and posted up in the sandpaper aisle for at least 3 hours.
Guy 2 - Ah, good old road jerk I assume?
Guy 1 - Why else would the crotch of my pants be stained red?
Guy 2 - Well I didn't want to be rude and point it, but ya I noticed it you sick fuck.