There are prohibitions against pride and immodesty. Some do get piercings and tatoos for the specific purpose of eliciting a sexual response in other people or for no other reason than to stand out in the crowd and get themselves noticed.
“Because it’s sexy” is nothing more than justification for putting a stumbling block in front of people who otherwise would not be drawn into lust and other forms of sexual tempation. “To express my individuality” is nothing more than pride.
It’s one thing to make oneself beautiful, especially for young woman for whome it is legitimate to want to attract a husband but modesty and humility are hallmarks of the Christian life and signs of holiness. You just don’t see too many monks and nuns running around with nose rings and tribal “body art.”
Appropriateness of the situation is important. A swimsuit may be appropriate for the beach but not in the office and similarly, a belly button ring and butt crack tattoo is innapropriate for Mass and strictly forbidden in my daughter’s School. Culture and time has a role to play as well. An African tribe is different from a business woman on Wall St.
If tatoo’s and peircings injure the virtues of pride and modesty, then they go too far. Ask yourself, does this tatoo, piercing, hair cut, way of dress, etc. say, “HEY EVERYONE, LOOK AT ME!” or will it cause members of the opposite sex to lust after me?
-Tim-