While on fire, above a bear trap, in front of a tripwire, inside of a box at a post office. And last but not least, "Never pass out... when markers are about" - Rigby (Regular Show)
after jumping out of the plane, but before deploying the parachute.
You can skydive without a parachute. You just can't do it twice. The worst place to fall asleep... in front of a moving train, on fire, with a robotic cod about to shoot you with a rocket launcher.
If your friends are pranksters, then it isn't wise to fall asleep while you're around a whole bunch of them. Falling asleep in an important class isn't good either.
If you are giving any type of speech When you are playing a sport At your job when you are a pilot or other jobs where people's lives are pretty much in your hands.
My perspective is there is never a wrong time to sleep. If you want to sleep then sleep, and don't let anything get in your way! Don't let anyone tell you when you can't sleep! This is your sleep we're talking about! YOU WANT SLEEP YOU HAVE TO TAKE IT FIGHTING! That is all.