Some of my "favorites"

Pennsylvanians who insist on coming to a complete stop on freeway on-ramps.

People who don't pull into an intersection for a left turn at a light that is not a green-arrow light.

Sicily -- Use of a turn signal depends on the age of the driver. Younger driver: Left turn signal means I'm turing left. Older driver: Left turn signal means I'm turning right and it's OK to pass me on the left.

California -- Their annoying habit of rolling down their window and sticking out their hands to signal you to wait for them to pull out or cut you off.

Finally, I wish US cars had rear fog lights like European cars.