It’s in their contracts of carriage: When you buy airfare, airlines do not “guarantee” a particular seat, schedule or flight. And airlines can be pretty persnickety about whom they fly and where they seat them. Back when I used to work for Eastern Air Lines, an employee flying on a company ticket had to wear a suit and tie in order to be accepted for transportation. We always flew in first class if there were seats, but one day I showed up at the check-in desk with a nice suit but no tie — and I was bumped back to economy. “The way you’re dressed, you don’t deserve to fly at all!” sniped the ticket agent.

Actress Andie MacDowell was, now famously, booted back to “tourist class” over the weekend for an equally silly reason: She carried a pet pooch on board. But because she was seated in the first-class bulkhead row, the dog and its carrier couldn’t fit under the seat in front of her. (There is no underseat storage in the first row of first class.)

Why the “Four Weddings and a Funeral” actress was sitting in that row while transporting an animal isn’t clear, but she was ignominiously booted back to an economy class seat. She wasn’t having it, and aired her thoughts on Twitter. “@AmericanAir HELP I paid for first class & they put me in tourist because of my dog that I pre-booked & paid for.”

But it’s not just airline employee dress codes and pets that can get you booted back to coach — or off the plane entirely.

1. The air marshal needs your seat.
These guys still fly to protect you, and they’re sometimes seated in first class without prior warning. If one of them shows up and needs your seat, you’ll either be bumped off the flight entirely or reassigned to economy class. And you won’t even get an explanation — obviously, the government doesn’t want you to blab that there’s an air marshal in seat 2A!

2. You pissed off a crew member.
When Bobby Abtahi, a Dallas attorney, was rushing through one of those large revolving doors at New York’s LaGuardia Airport, he supposedly “cut off” a Virgin America flight attendant who was attempting to enter at the same time. Abtahi was booted off his flight after the flight attendant complained to the captain of his plane. Virgin later apologized for the “misunderstanding” and refunded his fare.

3. You — or your child — won’t listen to crew member instructions.
Actually, if you do anything to annoy cabin crew or fail to obey their instructions and those “lighted placard signs.” When singer Sarah Blackwood of Walk Off the Earth couldn’t get her toddler to sit down and fasten his seatbelt just before takeoff, her United Airlines flight returned to the gate and both were invited to deplane. “That’s how babies are,” she reportedly said. Not a few other parents and their issue have been booted for unruly behavior — theirs or their progeny’s.

4. The airline oversells or double-books a seat.
Even in this era of sophisticated computer systems — or perhaps because of them — airlines oversell flights and even, on rare occasions, sell the same seat to two people. You’re now entitled to up to $1,350 in cash compensation if you’re “bumped” depending on the reason for the bump, the length of any delay caused and the price of your ticket. In 2013, Delta was fined $750,000 for, among other bumping violations, not informing passengers that they’re entitled to cash compensation rather than a travel voucher, and last year American paid a fine for similar infractions. The take-home message? Do not accept a travel voucher in place of the cash if this happens to you.

5. You’re not properly dressed.
Again, this is up to cabin crew, but if you wear a T-shirt with offensive wording, are exposing too much flesh, or are otherwise provocatively dressed, flight attendants and cockpit crew have been known to kick people off the plane. Spirit Airlines once deplaned a passenger for refusing to pull up his baggy, underwear-revealing pants, and Southwest has been known to refuse passage to passengers whose clothes reveal too much cleavage or other body parts. Thankfully, airlines no longer require employees to wear suits and ties when flying on company passes, but they’ll take it out on you if they don’t approve of your fashion sense.

6. You’re overweight?
In November, an Orange County man said he was kicked off an American Airlines flight for being overweight. According to press reports, Chris Shelley, who flies 100,000 miles per year in his job as an engineer, said an airline representative told him that “anyone over two inches in the seat cannot sit on the aircraft.” Ultimately, he convinced the woman next to him, whose complaint had prompted his ouster, to switch seats. American Airlines also sent out two apology emails and said it would investigate the situation.

This piece originally appeared in the New York Post. 

George Hobica is a syndicated travel journalist and founder of the low-airfare listing site Airfarewatchdog.com.