I've got nothing against anal sex btw, just I don't think it's amazing to around advertising you do it or at least love it from behind.
And what's it meant to be for? So the guy banging you from behind can look at it while he's doing you?
How does that work? The guy is thinking "yeah, yeah, fuck yeah, this is awesome. whoo!... yeah... actually this a bit boring... oooh what's this on here. A tattoo? Ah this will keep be entertained until I cum. Hmm, just some random meaningless squiggles, or something in Japanese. Wonder what it means? How interesting"
It might make be an ass, but I'd think less of a girl I liked and got to know and then found out she had one.
For me, I like naked female flesh, ideally I don't want it covered by some permament crappy scrawling. Maybe I just like girls to look "innocent"