A United Airlines passenger got "belligerent" with flight attendants. Here's what that will cost him.

Unruly behavior on airplanes can lead to hefty fines for passengers. 

Just ask Alexander Michael Dominic MacDonald, from Chelmsford, England, who this week was ordered to pay $20,638 to United Airlines for his outbursts on a flight from London to Newark, New Jersey, in March. 

The incident kicked off when MacDonald, 30, was having a loud argument with his girlfriend, according to an affidavit. The situation soon escalated and he started yelling at a flight attendant. He was both verbally and physically aggressive, according to court documents.