Where does the, presumably American, term 'fap' derive from??

@TexChik ☝️I thought it was women too🤔

@Montanamanguess we are still [i]rubbing one out[/i] 🤷🏻‍♀️

@TexChik Yes, this distinction as to the male supports the onomatopoeia theory, since the willy, particularly if intact, would more likely make said sound.