There are no high noon style confrontations; the people who would use a car or truck to harass a cyclist are the same types that will light the tail of a puppy on fire--they do it b/c they can get away with it. They aren't interested in letting you have a chance.
That's not 100% accurate. One of my co-workers was threatened by two tweekers in a pickup. He tried to ditch them but they chased him down into a parking lot. He got off his bike, got behind a concrete planter and started calling the cops. He also bluffed (rightly or wrongly) like he had a gun. They backed off but not w/o the obligatory "we'll find you and kill you!" remarks.
He bought a .38 the next day and took the course for his permit the same week.