The story so far concerns three items pronounced /fæp/:
(fæp-1) an exclamation of annoyance, similar to drat!
(fæp-2) an onomatopetic expression, representing the sound of vigorous male masturbation
(fæp-3) a verb meaning ‘to masturbate vigorously’ (of a man)
How do we spell these items? As far as I can tell, the first has only the simplest available spelling, FAP, but the sexual items show variation between FAP and FAPP. What to make of this?