BITES THE DUST
This phrase comes from the translation of the epic Greek poem the Iliad about the war between the Greeks and the Trojans. It was poetic way of describing the death of a warrior.
BORN WITH A SILVER SPOON IN YOUR MOUTH
Once when a child was christened it was traditional for the godparents to give a silver spoon as a gift (if they could afford it). However a child born in a rich family did not have to wait. He or she had it all from the start. They were 'born with a silver spoon in their mouth'.
A LONG SHOT
A long shot is an option with only a small chance of success. In the past guns were only accurate at short range. So a 'long shot' (fired over a long distance) only had a small chance of hitting its target.
MAD AS A HATTER
Some people say the phrase comes from the fact that in the 18th and 19th centuries hat makers used mercury nitrate in their work. Exposure to this chemical does indeed send you mad. However according to some people the origin of this phrase is much older. Hatter is a corruption of the Saxon word 'atter', which meant adder or viper. Furthermore 'mad' originally meant poisonous. So if you were mad as an atter you were as 'poisonous' (bad tempered or aggressive) as an atter (adder). It goes to show that often it is impossible to be certain where old sayings come from.