You have to be able to sit back and think about the driver of a car and the situation they're in.
Under normal conditions, when I drive, I'm paying attention to everybody else on the road. Now, as a cyclist, I pay extra attention to bikes on the road and try to give a little bit more leeway than most. But I'm going off on a tangant here...generally they're angry because they either aren't healthy due to their lifestyle or they've got 50 other things on their minds.
When I ride, I can clear my head and concentrate on me, even if I have problems to work out, they sort of just ebb away once I get my cadence up and enjoy the wind in my face, et al.
I'm not defending either side frankly, just realize that intolerance is really more a case of letting too many things collide internally while driving a 2 ton machine.