The catch is a dress code. But even for those paying regular fares, there is a dress policy, of sorts. United, Delta Air Lines and American Airlines all list bare feet as grounds for removal from flights in their official contract of carriage documents, for example. Those extra words, according to Brian Sumers, a reporter at the travel industry website Skift , mean that anyone who shows up in a T-shirt scrawled with profanity or a lewd message may be barred from a plane. Those in bikini tops may also have a problem, he said.