'Willie' is quite acceptable IMO and I could probably supply you with a dozen or more less acceptable euphemisms too.
Our English kanguage is rich and colourful and should never be censored or limited to basic scientific terms. I love the way words evolve and some are quite amusing, especially to the innocent and unwary.
I'll never forget nearly inhaling my tea when my late (and naive) MiL, talking about some VIP, declared him to be a 'big knob' 
Good Morning Friday 31st July 2026
Cookery books and other books - are you keeping them ?
Bonnie Blue the MSM should stop all reporting.
Daughter not allowed to know new baby’s name until she visits him



which reminds me of that wonderful Blue Peter clip at the door of some cathedral, admiring the medieval knocker. Much sniggering at that!