I got my tattoo (a rose) for a few reasons: 1, my name means "little rose" in Irish and 2, I knew this really great woman who was called Rose and she was one of the strongest people I've ever met, a true inspiration.
I have my lip pierced which is obviously very noticeable and I like it lots. I didn't get it cos I wanted to fit in, I guess I just wanted to form my own identity. My parents have been against it forever and they still are, but I didn't get it just to annoy them, I genuinely wanted it for years. And then when I could, I got it done. I want more piercings (tragus, septum and nipple being some of my choices and just cos I like them), and I have more tattoos in mind for when I can afford them. It's never been about fitting in though (for me, I can see how and why it would be for others). But like Amy said, it's as personal and expressive as the clothes you wear or the music you listen to.
...not sure if any of that is relevant.