The heart on my sleeve.
I'm 28 years old and have two tattoos, both of which were impulsive moments (and adrenaline rushes) I stressed about and don't regret at all.
When I was 18, I'd just graduated from high school, was a week or two away from moving to another state where I knew just about nobody for college, and in some way knew things were about to change. I was heavily overweight, fairly aggressive, and needed a change of pace. On my 18th birthday I went and got a TINY blue star tattooed on my left hip. Would I choose it today? Probably not. Did I feel totally empowered, independent and in control when I got it? Yes. I forget it's there all the time, and very few people have ever seen it. The blue is fading, it's fairly cliche, and now that color is one of my least favorites, but I still wouldn't change anything.
Last fall, about 10 years later, actually, I decided I wanted something on my wrist. My mom has always drawn hearts in place of signing things like "Love, Mom" on cards, notes, etc. They kind of look like a cross between a boomerang and a fortune cookie, but they're her signature and we all imitate it now. I got out every card and note I'd ever saved from my mom (about 15 of them), picked my favorite version of her "heart," and took it to a tattoo shop. Within about three hours I'd decided I wanted to do this, chosen the heart, and had it inked on my right wrist. The things you do with an afternoon off of work... I love that you can't really tell what it is, that it looks like I took a sharpie and scribbled on myself, that it's black and goes with everything, that I can cover it with a sleeve or watch if I so-choose, etc. Every time I look at it, I love it even more.
In my really preppy days in college I second-guessed getting the star, and in my totally professional days in Chicago I questioned whether the heart on my wrist would impose certain opinions and first impressions on me that I didn't want from others.
In the end, though, life is too short to worry about regretting something like that. I'm a designer and I love all things creative, pretty, and self-expressive. Both of these represent me, my style (at one point or another) and make me feel more whole / more like myself when I look at them.