The first time I ever did this was when I was relatively drunk. She was a conservative Thai/Issan chinese decent girl who'd had some wine and let her inhibitions melt off.
In moments like this, your pants are clawed off, the previously shy female is mawing at your cazzo with full oral aggression, and your own inhibitions are torn asunder by raw animal rage. Here's a caboose in your face, your netherlands alight with dripping fury, and you'll be damned if a bit of fecal fear is gonna put you off of matching passion. So you go in with the tongue. It's not a bad place to be.
Let's turn the tables, now. I've had many a girl--over 50%--make the foolhardy attempt to slide her tongue a few inches too far down. I'll tell you right now, ladies: you feel compelled to work beyond the cock, and it's not necessary. A little ball action is fine, but once you start delving into the taint and ass--and trust me, we can sense your hesitation here--you've overstepped your role. Unless you're being paid forget it. A man's ass is the last place you ever want to be.
Please be truthful and forcoming.