A person who derives sexual pleasure from surprising complete strangers by exposing themselves. A subspecies of an exhibitionist.

The stereotypical flasher is a dirty old man in a wrinkled, smelly mackintosh and pant legs (the lower half of a pair of pants, cut off at the knee and held up with a rubber band or elastic) who walks around town, flashing all of the girls and women he sees; but it can also be the woman who wears a too short skirt and no panties.