My manager tried to tell me I couldn't wear my earrings at work even though they weren't against the dress code
This was about 7 years ago, but I just remembered it this morning while putting on my earrings. I spent about 3 years working in auto part delivery and sales. I knew what I was doing and I was pretty good at it.
There was no uniform at my job, just to dress appropriately and be aware that there could be oil/battery acid so make sure you have backups. While at work I almost always wore plain t-shirts and jeans to be prepared for anything, so one of the ways I was able to express myself was my earrings. I never wore anything huge, but I liked to wear dangly ones or hoops, nothing huge but since I always had my hair back they were definitely noticeable. My manager would often make comments about them, and one day he flat out told me I had to them off (that day I was wearing ones that have 3 small silver keys dangling not even an inch off my lobe, nothing extravagant). I told him that didn't get in my face or affect my ability to do my job, so if he wanted me to take them off I wanted him to show me where in the dress code it said I couldn't wear them. Obviously there was no such rule in the dress code, but my boss was unhappy about it and ended up complaining to the owner of the company. When I got called in to talk to the owner I stood my ground that there was nothing wrong with them and he couldn't tell me to take them off just because my manager didn't like me wearing them. I ended up getting back to work, though we all know how bosses handle being told their wrong, so it was an awkward couple of weeks. It eventually blew over, but that instance just seemed so unnecessary.
Side note: this was the boss that hired my (male) friend about 8 months after I was hired at one dollar higher than my pay. My friend had at least a year less experience in the field than me and was hired for the same position. When I confronted him about our unequal pay he told me it was illegal to discuss pay, so I told him it was illegal to tell me I couldn't discuss pay (this is in the US). I ended up getting the pay raise, but there were several months that my friend had been paid at that higher rate that couldn't be made up for.
Moral of the story: know your rights! Speak up for yourself!