For the type of riding I do, parked cars are the biggest hazard. I got knocked off my bike once by someone opening their door – I just heard a bang, next thing I know I am lying on the road on my back, facing the way I had just come, with my bike about two metres away. I was clipped slightly and went over the bars. I was lucky not to be more seriously injured, but now I scan cars for occupants and give them a wide berth. Defensive cycling is definitely the key.
I do get the impression that most drivers do not enjoy driving however, and are in a state of continuous borderline anger and frustration. How else to explain the compulsive desire to accelerate madly out of one set of lights, only to brake ten metres down the road at the next set of lights. .