I only have one tattoo.
Back when I was living at the fraternity, a drunk brother came into my room while I was using a Koh-I-Noor graphic pen. Surprised, I accidentally stabbed myself near my right thumb. I've had a little black dot there for about 20 years. Technically, it is a tattoo.
Great fun at parties and bars, though. I tell women that I have a tattoo and that they'll never guess where it is.
It is slightly tempting to get a bunch of UV-sensitive ink that only shows up under a blacklight. That would totally freak people out, since I'm really clean-cut.