A tat should be a permanent, personal statement - a reflection of what you have inside. I don't care what a tattoo is, or how big or what color as long is it means something to the person sporting it. If a woman is a huge Roy Orbison fan and get a tattoo of Roy Orbison on her ass, then that's fucking awesome. Hell, even if she were a huge Adam Sandler fan and got a Roy Orbison tattoo on her ass as a cheeky nod to The Waterboy, then that'd be fine, too, because it's an important part of how she feels and her tattoo is a physical expression of that.
Now, if she (or anyone) had an Oakland Raiders logo tattoo but was actually a Browns fan, but liked how the Raiders logo looked, then IMO, that's stupid. A tattoo is a wonderful nonverbal signal - a billboard, if you will - a means to attract likeminded individuals. Therefore a tattoo should honestly communicate something about you. In Cap Katanga's example, the "Every Rose has a thorn" tattoo (to me) would signal: "I like late '80's power ballads, spandex pants and dirty men who smell like ashtrays." An obvious mismatch, and one that, like the Captain, as issue that could be dealt with ...later. But to someone else, that same tat could read "I enjoy the power and fury of a packed arena, the forlorn rhapsody in Axel's voice, and the raw, visceral impact of a solo performed by a guitar virtuouso like Slash." To someone, this woman could be soulmate material.
Even Coyote's example of #43 in Blue could be okay (I say that only for purposes of this post), if the image that is #43 in blue happens to hold some deep, personal significance to the person on which it will be inked. But like I think Coyote was going with that, a person who picks #43 in blue just because all her other dingbat friends are getting tattoos, that is just reprehensible.
To me, the bottom line is I'm all about personal expression, and a tattoo is one of the more powerful forms of it. Don't falsely advertise who you are.