You're the one who started the butt-play talk! I just hopped on board.
It's not about growing up tricky. It's about cleanliness. I am a super clean freak, dude. My house is pretty much immaculate, my car never has anything strewn about it, my office at work is surgical in it's precision, and feces is fucking dirrrrty. Not sure if you read on Thrashinc but twice now she has stuck her nose down in my gooch and inhaled deeply. I was a little disturbed at first because I didn't want her smelling near my asshole. I'd taken a shower beforehand but hell, you never know.
Yes, obviously women do all the same things guys do (shit, piss, fart, burp, puke). I just cannot imagine pulling my finger out of her asshole and smelling crap. Dude, I'd get limper than a gummy worm pretty much instantaneously and she'd see that, and feel self-conscious and it would just fuck it all up.