Frequent flier Howie Rappaport sees passengers protective to the extreme about their overhead bin space.
"It's as if all common sense just kind of goes away," said Rappaport, a product manager for a software company who lives in Savannah, Ga., and flies 150,000 miles a year.
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"I have asked people if I could move their bag (within the bin) and they have said no. So not only do people get frustrated, people have said, 'Don't touch my bag,' 'That isn't yours,' 'Go somewhere else.' People are downright rude."
The carry-on madness started as soon as U.S. airlines started charging travelers for checked bags five years ago, Keagle said. The fee may be hated by fliers, but it has turned into a revenue bonanza for the industry, with domestic carriers collecting almost $3.5 billion in baggage fees last year, according to the Bureau of Transportation Statistics. Among U.S. airlines, only JetBlue and Southwest do not charge for the first checked bag.
Then there are fliers like Rappaport, who doesn't check luggage because he doesn't want to wait for his bags after the flight. His grueling travel schedule means he has elite status on most airlines, so he always has priority boarding. Rappaport can't imagine traveling otherwise, observing that the tension starts right at the gate with "gate lice"—passengers who line up even before the boarding process starts—ready to pounce as soon as their zone is called, he said.
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Some travelers even try to break the rules.
Anne Banas, executive editor of SmarterTravel.com, said she saw a passenger trying to bring five carry-ons on a recent flight. (Airlines usually allow two: a small bag plus one personal item, such as a purse.)
She has also observed people boarding out of their zone to get an edge over other fliers.
"Often times when you get to your seat, you realize that the bin that's supposed to be yours is completely filled and then you have to scramble," Banas said.
"It becomes this whole nightmare. If we did travel with less, had more reasonable size luggage, one per person, there should be space for everybody, but it never seems to work out that way."
Keagle sees passengers employing all kinds of sneaky carry-on maneuvers. The one that drives her crazy is fliers cramming an obviously too-big bag into the overhead bin and then walking away, even though they know the bin will never shut. Often, when she asks people whose bag it is, no one will claim it until she loudly announces that it will have to be checked.
Even "Saturday Night Live" recently made fun of fliers boarding with "carry-ons that have no chance of fitting in the overhead compartment."
Another common strategy is for passengers sitting in the back of the plane to put their bags in the forward bins so they can just grab them on the way out, Keagle said, adding that flight attendants try to stop the practice.
During the holidays, when the flights are full and everything is chaotic, some passengers even try to hide bags underneath their legs and then throw their coats on top of their laps to try to hide the fact, Keagle said.
"You can tell because they look so squished in there," she noted.
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Don't be that person this holiday season. Here are some tips from the pros to help ease the battle of the bags:
Look into early boarding options: Some airlines offer priority boarding for a fee, and this is the time of year when it might be worth paying it, Banas said.
If you fly more than a few times a year, Rappaport recommends getting an airline-branded credit card that offers priority boarding.
Consider shipping your luggage: Depending on your airline's bag fees, it can cost more to ship your stuff, but it can make things more convenient and you get a tracking number so you have a bit more of a guarantee that your luggage is going to make it on time, Banas said.
Don't feel entitled to a spot in a bin: Many fliers think the overhead space right above their seat belongs to them, but that's actually not the case—it's purely on a first-come, first-serve basis, Keagle said.
Expect that you may have to check your bag: Pack your medications, necessities or any valuables in a carry-on that fits underneath the seat in front of you, because you will always have that space, Keagle said.
—By A. Pawlowski, NBC News contributor.