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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!!!
by kellyj2777 August 11, 2006