To preface, this was several years ago when I was in my late teens, and I didn't really realize it was a bit messed up until lately, so there's nothing I can do about it now.
This may be the opposite of what you'd expect (at least I've read stories of black employees being discriminated against like this) since in this case I was the only white employee at a convenience store in a city with the majority being black.
The manager got out the handbook pointing to part forbidding “exotic hairstyles.” Here's the thing: my hair wasn't styled at all, aside from brushing it. It was just straight brushed hair – apparently her problem was that it was long, somewhere just past my neck, with me being male.
At this point, I didn't actually know how to put my hair up in a ponytail. I know to most people with long hair it's as simple as tying shoes, but I wasn't used to having long hair – at this point my hair was only long because I used to go to my girlfriend's favorite salon with her and get my hair cut while hers was styled, and since she died I was too anxious to get a haircut since I knew she would've liked for me to go to that salon and I was too sad to go without her.
When my manager was throwing a fit about it and I said I didn't know how to put it up, she told me to turn around and she put it up for me. In hindsight I should've refused, as again my hair was just completely natural aside from being brushed and groomed and not “exotic”. Also FYI this store did not sell any fresh unpackaged food, no roller grills or anything, so it was never cited as a safety thing, they just didn't “agree” with the “style”.