Why can't we all get along?
Why do motorists get angry?
The other point to make about drivers getting annoyed at being held up and their willingness to overtake in dangerous places or very close to the cyclist is their impatience. No one wants to be held up and it annoys everyone but if motorists waited until it was safe to overtake instead or rush dangerously, they'd find that the time they are delayed by if they were stuck for a mile on a 30mph road is less than 2 minutes, in the scheme of things not really enough to risk someone else's life for in my opinion. Even things like overtaking when there is clearly stationary traffic ahead or before the driver has to make a left turn is displaying a disregard for the cyclist's safety to save the ten seconds or so it would take to wait behind them.
Motorists also get annoyed at cyclists jumping red lights, this in my opinion is justified. It is against the law for cyclists (as well as cars) to jump a red light, it's a very simple rule which a lot of cyclists seem to ignore. I don't have a defence for this as I don't think there is one, so if a cyclists creates a dangerous situation by jumping a red light and a motorist gets annoyed, I think they have every right to be. Cyclists also occasionally cycle on pavements or the wrong way on the road or down one way streets, these are also against the law and there is no real excuse for them either.