traveling on a buddy pass, i was once denied boarding for wearing peep-toe high-heel shoes. The GA interpreted the dress code of "covered shoes" to include 100% of the foot. He deemed my slight peep of a toe unacceptable. since I had my other shoes in checked luggage and he was boarding me as the last person before the gate closed, i didn't have time to buy/get other shoes. never mind that i was hanging around the gate for the previous 1 hr. oh well, lesson learned. i now always travel in completely closed shoes (when on buddy pass), which is a pain in the summer in tropical areas.
in that case, i had to go back and travel next day (this was in LHR).