Two women were removed from a JetBlue Airways plane for reportedly staring at a flight attendant.

The leader of a popular rock band was kicked off a Southwest Airlines flight for refusing to pull up his baggy pants.

A University of California, Berkeley student said he was booted from a Southwest flight for speaking Arabic.

Examples of passengers being removed from flights have gained increased attention since the Sept. 11, 2001, terrorist attacks, which began with the hijacking of four commercial planes. After the attacks, flight personnel suddenly found themselves focusing more attention on identifying potentially dangerous passengers than serving drinks and snacks.

“Nobody enjoys kicking passengers off planes,” said Heather Poole, a longtime flight attendant and author of a book about her job, titled “Cruising Attitude.” “Nobody wants to be the reason a flight is delayed.”

Airlines have the authority to boot passengers from planes under the contract of carriage, a lengthy agreement between passengers and airlines that includes a section about banned behavior.

Southwest Airlines’ contract of carriage, for instance, is 41 pages and has been revised multiple times, most recently in February. Such contracts usually are found online, and passengers consent when they buy an airline ticket.

Airline contracts usually describe prohibited passenger behavior in vague terms such as “disorderly,” “offensive,” “abusive” and “intimidating,” giving flight crew members the ultimate decision on what specific acts are out of bounds.

Flight attendants, who generally make the first assessment, said they worry that ignoring a potential problem passenger on the tarmac could lead to a bigger disturbance at 35,000 feet in the air that means diverting a flight.

Marian Bruns, a retired flight attendant from United Airlines and secretary-treasurer for the Retiree Association of Flight Attendants, said flight attendants take classes on the latest security measures and routinely undergo cultural sensitivity training.

Although flight attendants say they are placed in a difficult position determining which passengers could be a disturbance – or a threat – they say a passenger’s attitude often is what determines who gets kicked off. Such a decision frequently is made after conferring with other crew members and the pilot.

FAA data show that airlines reported unruly passengers on only 82 flights in 2015 out of about 9.6 million flights a year.