If you didn't blow up already (sometimes very hard.) and have the chance, gently tap their window an make a lowering gesture towards it. If the window opens explain in a calm voice how exactly the driver f-ed up and that his or her behavior almost or definitely ruined your day, bike, mood. Surprisingly, most of them understand their mistake and apologize immediately. Wish them a nice they and ride away. It is important that car drivers are not scared of cyclists otherwise they will never want to leave their car and ride a bike. It is also equally important to let them know that they can't get away with doing stupid/careless things otherwise they will keep doing them.