A bum willy is a term used for a man who has a below average cock size of 4 inches, where the woman feels the need to stick it in her bum as a last resort for any sort of feeling or pleasure during sex.
âOh god I met a guy last night who had a Bumwilly the sex was abysmal.â
âI need to find a guy with a Bum willy so I can have comfortable anal sex.â
âThe sex was so mediocre last night I had to stick it in my bum.â