A Hair’s Breadth Meaning: An tiny margin or amount.
Keep Your Shirt On Meaning: Keeping calm. Usually said by someone who is trying to avoid making others upset.
Fool's Gold Meaning: Iron pyrities is a worthless mineral that resembles gold.
Back to Square One Meaning: To go back to the beginning; back to the drawing board.
Short End of the Stick Meaning: Getting the bad end of a deal, or receiving the least desirable outcome from something.