Picture thousands of stressed-out holiday travelers in airport terminals, train stations and bus terminals, all piling into a claustrophobia-inducing cattle-class cabin, with luggage.
"The worst offenders are people who abuse the carry-on luggage limit and take up more space than they are supposed to get," says Raymond Lee, a finance director for a consumer goods company in New York and a frequent traveler.
"They are also the ones who will put their luggage sideways and take up more space for no reason other than they just don't care to do it right."
But don't take his word for it. Simply board a flight, grab a seat and watch. Chances are, you'll see a fellow passenger try to wedge a too-large carry-on into an overhead bin, or a passenger with a backpack whacking another traveler, or two people bickering over the space under their seats.
What better time to brush up on your luggage etiquette and learn a defensive maneuver or two?
It starts with what you bring. "Consumers are looking for the most possible space and lightest-weight case possible," says Scott Niekelski, a direct import manager at the National Luggage Dealers Association, a luggage distributor.
When it comes to proper luggage etiquette - less is more. The most experienced passengers travel light. Some don't bring any luggage.
"I ship my gear ahead to my destination, especially if I plan to be in one place for an extended period," says Brian Teeter, the Irvine, California, author of the "Healthy Trekking Travel Guides" series.
Having no luggage is probably the only way to ensure you'll never fight about it. But let's be realistic: Most of us travel with at least a backpack, purse or some other kind of carry-on.
Here are some luggage etiquette to follow:
*Downsize to a smaller carry-on or a backpack, and place it in the bin above your seat - not someone else's (that's called bin-hogging.
*Don't overstuff your bag to the point where you have to wrestle it into the compartment. "Stow carry-on luggage quickly in the overhead bin so other passengers may pass in the aisle," says Rachel Wagner, a corporate etiquette consultant in Tulsa, Oklahoma. "If you need extra time to stow it, step into the seat area for a moment so others may pass by, then step back into the aisle when there's a short break in the aisle."
*No one likes a blocker, and that's true at the luggage carousel, as well. Consider the mad dash for the best position. For some reason, passengers feel they own the spot immediately next to the conveyor belt, and they refuse to give it up for anyone, even if those people see their luggage and want to collect it.
*Backpacks are another source of pain for travelers, and that's true not only on planes but also buses, trains or any mode of transportation with narrow corridors. During boarding and deplaning, it's easy to turn quickly and unwittingly hit fellow passengers with them.
*Parents, if you can avoid taking a stroller, do. Strollers are clunky and they're easily damaged when you gate-check them. Also monitor older kids with luggage.
*Don't let children wheel their own suitcases through the airport, says Evie Granville, a political campaign manager from Houston who hosts a lifestyle podcast that often deals with etiquette issues. She recommends packing a backpack for them.
Luggage etiquette is only a partial solution to the seasonal squeeze. You have to also play defense. Watch out for the backpacks, the passengers with the overstuffed bags, the moms and dads with strollers and, yes, the tweens with wheeled luggage. Don't assume they have the same good manners you do.