Planes, Trains & Automobiles taught me that if you for whatever reason sleep in the same bed as another man don't assume you have your hand between two pillows when you wake up.
If you ever find yourself in the Vietnam War with a badly injured buddy who's begging you to put him out of his misery, you'd better do it. Otherwise he might blame you for letting the Viet Cong capture him and return years later as a pissed off bent on revenge.
I learned if you ever capture Chuck Norris just kill him as fast as possible because he makes one pissed off POW and he will escape and beat your butt and then blow you up.