What do you do When you approach car using their high beams you should?

Reduce speed (because you can not see properly) by releasing the accelerator/gas pedal. Place your foot over/on the brake pedal but do not brake (cars behind you are also unable to see properly, and may fail to see your brake lights.) Flash your high-beams briefly, once, in the hope that this prompts the other driver to dip theirs. If this does not work allow your vehicle to continue to slow naturally and without the use of the brakes, paying attention to keeping your vehicle on the correct side of the road. If possible, and room allows, move closer to the curb-side of the road, to give the other car as much room as possible. Once the other vehicle, and its probably DUI driver has passed give them a mental One Fingered Salute, and continue on your journey.