I wear whatever the fuck I want. I once had a sort of boss (not a line manager just a coordinator. Our team were all contractors and didn't really report to one person as such). She saw me crossing the office one day and pulled me aside to tell me I had to wear a shirt and tie from now on. Anyway, I just said "nope", and walked off.

She had been trying shit like this on our team for a while and we knew we could just ignore her about this stuff. Still satisfying though.