There are some things that everyone just does, even though we've never been told to, and certainly we've never been told why. I always let people take what fries they want from my plate, because that's a lot of potatoes, and the hamburger will fill me up by itself. But if I order onion rings, suddenly everyone wants one, and there aren't that many in a serving!
Well, of course I'm going to get nervous even though I've done nothing wrong. I'm nervous because a team of strangers is going to put me in a machine to see what my body looks like under my clothes, or else they will grope me. Or like the last time I went through security, both. (My teenage daughter got neither, because that would be "wrong.") However, there are a couple of "unwritten rules" in this list that you WISH people would follow.
See the rest of the 19 unwritten rules that everyone seems to follow in the latest pictofacts list at Cracked.