I would have to know the girl for a while before I went down on her. Who knows what's been up there. A guy who goes down on some gal he just picked up in a bar is nuts. I don't care if I find her in a high-class bar and she looks like Ivanka's hotter cousin, wearing a Gucci dress and pearls. First off, if she lets me take her home and go down on her on the first pick up, then I know something is wrong.
And I am assuming the gal must not be an ass virgin, because this was spontaneous buttsechs, and I am assuming no condom, no lube, no warning or foreplay. Something like that would have sent most women into shock and caused them to scream like a Banshee and to walk home pidgin-toed and with their crotch projected about a foot in front of the rest of their body, with both of her hands planted firmly on her butt, going "ouch, ouch, ouch, ouch" with every step. For her to say it did not hurt tells me she has gotten it in the backdoor a lot. A lot. Or the guy had a really small penis.
So if this guy is crazy enough to go down on a complete stranger he just met, and he goes raw dogging her in the butt, that tells me he is probably a psychopath. Living dangerously, I tell ya!