Billie Joe Armstrong, the lead singer of the band Green Day, has just fallen foul of this little-known dress code.
He was ejected from a plane at Oakland airport after a stewardess became upset that his jeans were “sagging” to reveal his underpants.
The incident took place on a taxi-ing flight bound for Burbank, in Southern California. It prompted Armstrong to vent his frustration via Twitter. “Just got kicked-off a Southwest flight because my pants sagged too low,” he told 170,000 followers. “What the f**k? No joke!”
An eye-witness, Cindy Qiu, yesterday told TV news teams that the incident, which took place last Thursday, occurred after the extravagantly-attired performer boarded the flight late.
As he walked to his seat, a hostess primly asked him to pull his trousers up.
“Don’t you have better things to do than worry about that?” came Armstrong’s response. Shortly afterwards, he was escorted from the aeroplane.
When Southwest had become aware of exactly who Mr Armstrong is – Green Day has sold over 65 million records, and their album American Idiot swept the Grammys – they offered to re-seat him on a later flight.
The affair raises many questions. Are exposed underpants offensive? If so, do US airlines have the right to subvert free expression by banning them? And why was Armstrong, at the age of 39, adopting a sartorial code popularised by middle-class teenagers?
Either way, the singer - isn’t the first celebrity to regret travelling via Southwest, the US equivalent of Easyjet.
Last year, the well-lunched film director Kevin Smith was ejected from one of their flights after being told he was too wide to fit into the single seat he’d purchased.