You get a shock when you get out and touch the car on a hot day
My answer :
Touch the ground first, with your hand or your shoeless foot, to 'discharge' the static shock that has built up in you
More info
It's static charge that has built up inyou. Usually on a hot day, probably when you are wearing rubber sole footwear. The static charge builds up in you and can't get through to earth because of your rubber soles. When you touch the car it goes to earth completely via your finger through the car. If you touch the ground first with hand or shoeless foot, the charge goes to earth that way instead and is discharged over a wider area, so you don't feel it.
