There are some things you can count on. Sure, there's death and taxes, but on an airplane you can trust there will be little space to stretch your legs (if you're in coach). 

That fact has led a few people to punch their fellow passengers over the four inches they have. 

"Fistfights over the right to recline caused three flights to be diverted and forced to make unscheduled landings in a two-week period," write Christopher Buccafusco and Chris Sprigman in an article for Slate. 

Economics could provide some kind of solution to the problem. Buccafusco is an associate professor at the IIT Chicago Kent College of Law and has been studying the economics of reclining seats.

"We wanted to see what could actually get people to make transactions that would improve their welfare, make each person better off in these kinds of cases, so we encouraged them to barter," says Buccafusco.

The question: Would you offer or accept $8 for the right to recline? The answer was no.

"Instead, if you offer them a drink or a snack, the percentage of people who would be willing to accept such an offer went way up," Buccafusco says. "So, it seems like there's an opportunity here for people to be both polite to one another and increase welfare."

Read the full story: Who Deserves Those 4 Inches of Airplane Seat Space?