Asking Questions Correctly

Long years ago when I was teaching, I used to coach students on how to ask questions correctly. I would tell them: "Several times over the course of the school year, I will come here with visibly shorter hair. Try not to say something like,  "Did you get a haircut?", which is questioning the obvious, or worse, "What did you do to your hair?" which is vaguely insulting.
Some of the kids had never considered how to phrase a question so it doesn't sound like an accusation, and some concluded I had deep-seated feelings of shame connected with my hair. They were hilariously careful about commenting on my haircuts every six weeks, but it was a good lesson in thinking before we speak.
The world would run smoother if we learned to ask questions only when necessary and then considered how to ask for information without sounding nosy, judgmental, and insulting.
Around the world, Americans are known for being intrusive, possibly because we have such an open culture. We ask total strangers about their jobs, their spouses, their homes, and their kids without ever considering they might not want to talk about them. We're pretty forgiving of the foibles of others, so it isn't a big risk to answer, but do we really need to know the details of someone's life we meet on a train and might never see again?
Our media has made the intrusive question into an art form, from "How did you feel when your house exploded with your three children inside?" to "What's under that designer dress, Miss X?" One hopes most Americans wouldn't ask those questions if they were the ones standing there with a mic, but we tolerate such absurdities. Can we not empathize with how a parent feels without watching him sob out an answer? Do we need to know what some celebrity wears under her insanely expensive clothing?
Spouses are often guilty of asking questions in rude ways, like demanding, "Where did you put my check?" The implication is that one's spouse hid a slip of paper somewhere, maybe as the opening play in a new game. What's wrong with, "Have you seen that check we got in the mail the other day?"
Mothers-in-law can be masters of the innocent but oh, so insinuating question. If I wear anything more revealing than a mock turtleneck shirt, mine asks, "Aren't you cold, dear?" 
Then there are the dreaded questions we get when we've had surgery, an accident, or something else that shows us in an unusual state. "What did you do?" is the common question, as if we chose to fall down those stairs. 
Often a comment is better than a question. "That looks uncomfortable," allows a person to explain if he wants to or simply respond, "Yes, it is," and go on to some other topic.
Questions are useful critters. If we need to know something, we should form a query neutrally, without sounding like the other person is stupid, contrary, or has done something incomprehensible. 
If we don't need to know, we shouldn't ask.