The automotive version of a badonkadonk, it is the large rear end of a car. Can be easily spotted in parking lots, as the trunk (with junk or without) will take up far more of the aisle than would be considered safe. The driver might have to back out twice to avoid a vehicular booty-bump.
If I back up over your mother, it's not my fault. I can barely see over this car's fat bahonkahonk.