En español | We're all aware of the very reasonable Federal Aviation Administration no-nos that prohibit weapons, smoking and "interference" with airline personnel. But the airlines have their own rules, too. Some are less than obvious or a bit vague, and all are open to interpretation by and enforceable at the discretion of the crew. Let's count the many things that might get you banned from boarding or booted from a flight before takeoff:

Removing your shoes may sound like a good idea, but it could get you booted from the plane. — Ghislain & Marie David de Lossy/Getty Images

1. Smelling like a locker room
Buying a ticket contractually obligates you to refrain from boarding in "a malodorous condition." If you run out of time for a shower before your flight, at least take a sponge bath, just to be safe.

2. Bringing your germs onboard
If you appear seriously ill — especially with a condition that seems contagious — and can't produce a doctor's written permission to travel, you may not be allowed to fly.

3. Dressing inappropriately
Revealing clothing — including baggy pants hanging south of the undershorts — and T-shirts broadcasting lewd sayings or inflammatory political slogans have gotten passengers ousted.

4. Swearing like a longshoreman
Numerous conflicts during boarding that could have been resolved quickly ended instead with passengers being escorted off the plane when the fray escalated into a volley of foul epithets.

5. Showing up over-lubricated
A wee dram might relieve travel stress, but just appearing to be intoxicated is grounds for ejection. Even if you're well below the legal limit, be sure your conduct is unassailable when you have alcohol on your breath.

6. Public displays of affection
Thanks to crowded flights with cramped seats, very little goes unnoticed by your fellow passengers on an airplane. So you're better off saving any overtly enthusiastic displays of affection for your hotel room.

Next Page: Refusing to turn off electronics and other in-flight no-nos