An undercown is that shot in porn where all you see is the dude's asshole, and balls, often switched to right after some hot and heavy action, in order to make the viewer dump his load to the view of a man's sweaty balls
I was jackin it to some pron last night and right before I came they switched to an undercrown ... Am I gay now?
1. happening or existing without the knowledge of someone specified —usually used with to <unbeknownst to us rumors were flying> (Merriam-Webster Online).
2. a word that pretentious pricks use to try to sound smarter than they actually are.