Tattoos, piercings and body modifications: why?

[Albertosaurus Rex]

I suppose I can... kind of see why people take tattoos, but I have to ask: isn't the permanence of the thing a little scary? I imagine that a tattoo design is not chosen lightly.

What I don't understand at all, however, are piercing. Little rings or nubs of metal through your skin? I don't see the beauty in that - I don't want to offend anyone, but when I see someone with a head full of metal walk by, it revulses me a bit. And that's not even getting into more intimate places - I remember a girl I knew a few years back who told me and a few friends ecstatically that she had her left nipple pierced. I mean, what the hell? Similarly, getting one's tongue pierced just sounds painful and inconvenient. To say nothing of pierced genitals...

Although I would never want a tattoo, I can sort of understand why. But piercings? Part of me is convinced that it must be a symptom of something - a healthy person does not stick pieces of metal through his or her sensitive areas.