exhibitionist; flasher
Refers to a person who derives sexual pleasure from exposing their genitals in public. Often used in legal or psychological contexts, but also colloquially.
There was a report that a flasher appeared in the park.
He is receiving treatment for exhibitionism.
Compound of 露出 (exposure) and 狂 (mania, madness), literally 'exposure mania'. The exact historical derivation is uncertain, but the term likely emerged in modern Japanese to describe exhibitionistic behavior.