I'm usually pretty open about the fact that I pull my hair out. I'd rather just tell people that it's a condition rather than let them speculate. I guess I started yanking at my eyebrows when I was around 11. I liked the way it felt to yank the little hairs out, and I liked feeling the smooth skin underneath. But then I had no more eyebrows, and I looked pretty ridiculous for a while (moreso than usual, anyway). But they grew back, and I started yanking out the hair on my scalp. I'd usually pull like behind my ears or on the underside, so it wasn't as prominent... unless I lifted up my hair. Around 7th grade, I ended up pulling out half my hair. It was really bad. And it became more obvious when the hair started growing back in and was all spiky and different lengths and stuff. After that, it wasn't nearly as bad. I'd still pull from certain patches, but I learned that it was an actual condition (I don't remember when/how I learned, but it was probably when I was browsing the internet when I was 14-15). I even gave a couple presentations on it in my high school classes. At one point in college, I had a couple bare patches around my temples, but right now the trich is... I guess as dormant as it gets.
I seem to have a chronic "widened" part with spiky regrowth, and that's where I usually pull (mostly the regrowth). I also have a habit of hunting for split ends and breaking them off, but that's just because I refuse to get a haircut and even things out. (I've ALWAYS hated haircuts, especially since they touch your neck a lot, and I can't stand that sensation.) It's been that way for maybe 5 years now, and I'm fine with it that way. Just as long as I don't have huge bald spots any more.
Once I got to college, I actually met a bunch of people who also pulled their hair. They were usually friends or friends-of-friends who admitted to it if I told them about it. I've talked to a bunch of people online too (including a couple guys, which was interesting, since this affects mostly females). It's a lot more widespread than you'd think. But some people are good at hiding it, and you'd never know by looking at them unless you know what to look for.
The one thing that irritates me is when people try to be helpful by saying "don't pull your hair!" That's just annoying. My hands are in my hair all the time, but most of the time, I'm just fiddling and not even pulling. I love the way hair feels, so I twirl it around my fingers and stuff. I usually only rip out the hair when I'm alone, anyway. And telling me to stop won't make me stop. The best way to be helpful is just to listen to what I say, understand what it is, and then keep your mouth shut unless you have questions or non-critical comments that might actually be helpful. Yes, I know it makes my hair look funny. Yes, I know I shouldn't be pulling. No, I can't stop. There's nothing you can say or do that will make me stop. We all have our issues. I won't comment on yours if you don't comment on mine.