Zipper Bumping 

male becomes erect enough that his penis is pressed against the zipper of his pants.

Yo Ming! you see those two asian school girls making out on the bus, got me straight up zipper bumping....ya digggggg?

Zipper Bumping by RidiculousIsHe February 27, 2015

bumping zippers

1. Lovers knocking into each other when in a rush to get both of their pants off to proceed with a hot make-out session.

Attempting to get their pants off quickly during the passionate heat of kissing on the boat, Sebastian and Nicollete were eagerly bumping zippers.

bumping zippers by ThegirlDJ October 18, 2007