Well. Not so much 'fiddling' as general yanking, showing us all how impressively he can make it grow in size, wrapping it round the back of his neck and pointing out the 'nut' that is hidden inside.
I suppose I imagined I'd have had to address this earlier with DSs 1 and 2, but no, it takes DS3 to educate me. I have no idea what to say so could I have the Standard Issue MN recommendations please.
I've been muttering 'willies are for playing with in bedrooms', somewhat without conviction, under my breath. He just laughs and contorts further.