Since buying my 11 year old son a book about puberty he and his friend spend their lives giggling about the list of words for penis (including the word 'penis' actually (?) that are listed therein. It's quite harmless, and they spend their time giggling and randomly saying things like 'trousersnake' (their favourite) and 'John Thomas' like they have willy-tourettes. They crossed the line with 'piss-pump' though and got a severe look and raised eyebrow ?
Anyway, I like to keep one step ahead, so as many words as we can think of, please. And, bless them, if you say 'vagina' they blush up to the roots of their hair and cringe ?