If someone is literally head and shoulders taller than another person in height, it would be obvious. There would be no dispute as to who is taller. Taken figuratively, it would mean that another person or thing is indisputably much better than the rest.
I believe that the phrase refers back to a description of Saul who was described in 1 Samuel 9:1-2 as "a handsome young man. There was not a man among the people of Israel more handsome than he; from his shoulders upward he was taller than any of the people."
Nothing. The correct expression is HEAD AND SHOULDERS above the crowd - it's as if you were so tall that you were that far above everyone else.
Stay calm
An idiom is something that does not mean what the phrase says literally, so yes. You can't actually laugh your head off.
To turn completely around and head back in the direction you came from.
If used as an idiom, it usually means that you are confused about something. The image is of you scratching your head to try to think better.
If you have a good head on your shoulders, think what that could mean. Your head is where your brain is. If you have a good brain, you must be able to think pretty well. So having a good head on your shoulders means you're a good thinker.
If you are "head and shoulders above" the crowd, then you are taller than everyone else. In idiomatic usage, this means that you really stand out, you are better than the rest, you are noticeable in a good way.
Nothing. The correct expression is HEAD AND SHOULDERS above the crowd - it's as if you were so tall that you were that far above everyone else.
"My head is on my shoulders" means they are thinking right, they have their head in the right place.
If something is "above" your understanding, it is too difficult for you to understand. The image is of something just out of your reach, over your head. You try to understand it, but you cannot.
The head person.
Stay calm
An idiom is something that does not mean what the phrase says literally, so yes. You can't actually laugh your head off.
To draw is to pull something. He pulled his head in toward his shoulders, like he was hunching his shoulders up to protect his neck.
"Dive in head first" is to rush into a situation without thinking.
I don't know what you mean by "common phrases of," but the idiom "over and above" just means "more than what was agreed upon."
A bust in modeling would mean a head and shoulders figure.