One who waits around in public or private bathrooms, waiting for men or women to walk in. From then on, the person who enters the lavatory is free to do to said bathroom slut as they please, because a bathroom slut will do anything to a person. Nothing is out of bounds for a bathroom slut, as long as the act stays within the bathroom. After such act is committed, the person that originally entered can leave freely without any ties to the bathroom slut. The bathroom slut now just has to wait for his/her next contender AKA the next person to walk into the bathroom.
Zoe- Oh my god, did you hear about what that bathroom slut did to grandma at that gas station?
Francis- I know, I don't think grandma will be able to walk in a straight line for weeks!