Scotcop,
Maybe you should remind your supervisor that Jesus didn't wear pants. If your bookstore sells any Celtic stuff I would have some of your kilted friends come into shop, bring it all up to the register and then ask if this was the place where a guy wasn't allowed to wear a tartan kilt on National Tartan Day and when they said "yes", leave everything at the register and then walk away. Since you had permission from a higher up than you should have stood your ground. I wore my tan Utilikilt to work Tuesday as it fits in with our dress code but I wore a shirt and tartan tie. Usually the shirt and tie is for salaried managers so a lot of customers came to me to complain about stuff. None of the "real" managers said anything to me about it. I had one old lady who works there who is known to be a bully and tattle tail make a snide remark about me dressing up when I wasn't a manager and I just ignored the old crone.