People who have short arms may say their backs.
Others may say the center of the heel of their foot.
For me, it's gotta be the inside of the ears!
Over the years, I've tried to find the perfect scratching treatment for my inner-ears: Pen lids, toothpicks, bobbie pins, the back of a pen, Q-tips, and fingers (minus the thumb). For me, the thing that works the best is a metal paper clip that I stretch out and make long. Still, the itch always comes back.
I suppose I'll have to waith for the new system to have itch-free ears.