I've found whenever people give me crap about something (although not about my tattoo yet, since it's small and not super noticeable), I say something friendly, but pointed about how they should worry about themselves (I tell my students to worry about themselves when they tattle and I wish I could do the same with adults).
For instance, to the lady at the store--"oh, I just felt like my temple needed a little decoration" or "well, it's good you haven't gotten any then!" in a nice, friendly way--not sarcastically. Stuff like that seems to really knock people over and make them think about their assumptions and about keeping them to themselves.
Also... teacher to teacher (I'm just starting my M. Ed), what is your sense of how schools view tattooed teachers? My former school was pretty cool and I've talked to other teachers--but I'd like to get more perspectives on the subject.