CHICAGO (CBS) — Spirit Airlines – the discount carrier that touts its “ultra low fares” – kicked a passenger off a plane at O’Hare International Airport over the weekend after he tried to board wearing ultra-low pants.

As WBBM Newsradio’s Steve Miller reports, the man and a female companion were boarding a Spirit flight to Orlando, Fla.

LISTEN: WBBM Newsradio’s Steve Miller reports

And as they boarded, a flight attendant asked the man to pull up his pants.

Spirit Airlines spokeswoman Misty Pinson tells Newsradio: “It was to the point where his entire bottom was hanging out. And that’s not appropriate. We have a lot of customers on the plane, a lot of children on the plane.”

Pinson says bare skin was not showing. But his underwear was.

“Our flight attendant asked him if he would kindly pull (his pants) up so that they were at a more appropriate level,” Pinson said.

But the sagging pants were not the reason the man was ultimately kicked off the plane. It was what happened when he refused.

“He became aggressive with the flight crew,” Pinson said. “He threatened to smack the flight attendants.”

As far as what constitutes appropriate attire, Pinson says flight attendants are trained to use their own judgment.

The only specific mention in Spirit’s code is no bare feet.