I had a Catholic school friend who was threatened with suspension because of wearing patent leather shoes (for just the reasons mentioned by others here), but I had no idea this was such a common presumption. A girl I knew who grew up in Alaska once got in trouble for wearing trousers to her high school; the dress code specified that girls had to wear skirts, whatever the weather. On the day she was sent home in her trousers, it was way below zero with a terrific wind chill factor. She went back to school in her skirt -- and four pairs of tights.
The high school I went to had its share of clueless teachers, stupid rules, and daft administrators, but after hearing my friends' stories and reading all these comments, I think I got off easy.