Part of it was the whole process of being tested. My IQ test scores ranged from 120s to well over 200. Even as a middle school kid I understood the concept that if your tests measure the exact same quality and get wildly varying results, your tests are worthless. (For that matter, if you can't tell if a child is "gifted" or "disabled" without running tests, why the hell should I trust you to run tests?) Then, once they decide I'm not an idiot or afflicted with ADHD (they called it hyperactive disorder back then) they want to run further tests to "pattern" me. The obvious intent is to find a box in which to put me, a framework within which to respond to me. But I'm the same kid either way. Once they have you in a box, they respond to you according to that box; the exact same actions or words are interpreted differently depending on which box you get put in. Since no classification system can match every person and remain remotely useful, it stands to reason that at least a large part of the time the classification will result in an incorrect response. It's not a binary world, it's a very aggressively analog world.
I'm a pretty sharp guy. I'm also an only child raised way the hell out in the sticks - we didn't even have indoor plumbing until about the time I started school. And I didn't have a lot of chores. So I read a lot, everything I could get my hands on, and my parents encouraged it. Had I not been a reader, had I more opportunity for playmates, or less access to books, or enough chores to eat up my free time, I would have been exactly as smart, but I would have known many fewer things. Consequently I would have been treated quite differently, especially because I was almost totally face blind. (My vision was 20/200, which didn't help.) Seeing what happened to the kids not judged gifted was a pretty strong reason to dislike being classified at all. Once you're in a box, it's hard to get out.
For the rest of it, I considered it a waste of time, and it was about three days' worth on top of two weeks of IQ tests. There's so much to see, do, read. So many people to talk with. And virtually all of that is more interesting than myself. I'm just not that exceptional, and figuring out my various "classifications" is B-O-R-I-N-G.