From Longman Dictionary of Contemporary Englishflasherflash‧er /ˈflæʃə $ -ər/ noun [countable] SYSCCa man who shows his sexual organs to women in public → flash
Examples from the Corpus
flasher• Scarcely used is the compass, the flasher and the watch.• It was your average London park, complete with flasher, park-keeper, geraniums, a bum-splintering see-saw and baby swings. 