The worst, the absolute worst thing I ever did to my hair was when I used a home straightener on it in my ongoing attempt at getting a pixie style. I hated the way my hair turned out. It seemed dead. It just lay there and was impossible to style or do anything with.
My 2 funny/ironic mistakes were:
1. As a teenager, I taped my hair down to get it to dry straight. This was the 60's, the era of Dippity-Do hair gel and juice can rollers. I would smear Dippity-Do on my hair then tape it as straight as I possibly could get it so it would dry in my so desired pixie. When I went to remove the tape, the short hairs extending past the tape had curled and it looked like the tape had grown eyelashes, when I removed the tape, the rest of my hair would form waves all over my head. Looking back on it I think it was kind of cute how hard my hair was trying to make me realize the reality that it was curly, at the time I was disgusted at the "failure" of my hair to live up to my expectations.
2.Over the years, I have gotten several perms to get soft curls. They always (with just 1 exception) turned out "poodle" like. Now, on good hair days, my hair looks just like I was getting those perms to "force" it to look.
Now, I just wish I had relaxed and let my hair do its own thing long ago.
Experimenting with too many products to name here. All this great info keeps my head spinning.