When you need to pee but you're too lazy to get up from your computer or your couch so you hold it in for later until you feel like you're about to pee in your pants if you don't.
Emily: I need to pee.
Connie: Then go pee.
Emily: I'm too lazy to get up and go to the bathroom right now, I'll do it later.
Connie: Peecrastination is bad for your bladder, you know.
A mode of procrastination in which the individual, usually a student, in an effort to avoid starting homework, will go to the bathroom. Actual need to pee is irrelevant.
Jane: Ugh, I really don't want to start this paper. I guess I'll just go to the bathroom.
Jane's Roommate: Girl, you better stop peecrastinating!