It can have different meanings depending on the situation, but the usual meaning of "Pull up to my bumper" means to drive up your car close enough to my car so that it almost touches the bumper (rubber or metal bar that absorbs a car impact) or the back of my car. You might use this expression when you are trying to make sure there is enough space for everyone to park.
As for the meaning of the expression in song lyrics, it is a little more suggestive... Ha, ha.