After all, even the most capable passenger can be incapacitated by one drink too many, which could put lives at risk. They also note that it's unwise to sleep in the emergency exit row. Because, well, it's the emergency exit row. Another unwritten no-no: XL fliers.

Yes, you are permitted to sleep in an emergency exit row during a flight, but you must be able to wake up and perform your duties immediately in the event of an emergency. Most airlines do not have a "no sleeping" rule for these rows, as they are often sold as "extra legroom" seats for long-haul travel. However, the FAA and international safety rules mandate that passengers in these seats must be "able-bodied" and willing to assist the crew. If you are a very heavy sleeper or use sleep medication that makes you difficult to rouse, the crew may ask you to move to a different seat for safety reasons. Furthermore, you cannot use footrests, large pillows, or blankets that might obstruct the exit path while you sleep. During takeoff and landing—the most critical phases—you must be fully awake, alert, and your seat must be in the upright position, with all personal items stowed securely in the overhead bins.