The act of using your vehicle
as support (and/or to block your bare ass
from view) when you can't make it to a "real" restroom
and instead have to use the side of the road as a toilet
. Can be the result of either an emergency or laziness and is preferably done in a secluded place.
Earlene drank her Boone's wine so fast on the way to the party that we had to stop and let her bumper-pee at least three times before we even got there.
I can't hold it to the next rest stop -- you're gonna have to stop and let me bumper-pee or I'm gonna wet my pants in your car!!!