Left foot brakers who have their foot hovering over the pedal. Brake lights keep flashing on especially on highways. You don't know if they are really braking or not.
Ones who put the brakes on and then 100 yds. later signal a turn.
Tailgaters when there is no where for anybody to go.
The ones who will not dim their high beams.
Many years ago we had a rally VW. Standard lights not great so people ignored you flashing the high beams at them. Then the 3 driving lights would come on, one at time as we had a switch for each. Only twice had to use the windshield mounted adjustable spotlight. That worked as the beam searched them out.