I'll start by saying it's not everyone by any means, the vast majority of motorists are patient and go on with their day. We make an effort to disrupt traffic a little as possible, use mostly very quite roads (because cycling those is far mor pleasant) and pull over often to let traffic pass, but it is occasionally necessary to use a busier road for small part of the route.
However, I rarely go on a bike ride without one person thinking they need to hurl abuse. The most frequent situation is when they've tried to overtake me on a bend and come face to face with another car, which is apparently my fault.
The most recent occasion was down a steep hill, we would have been doing at 25mph, speed limit 40, So yes we were slow and it was difficult to pass but not that slow. Traffic lights at the bottom and driver felt the need to stick his head out and yell something about how we should be on the pavement (Yes of course we should doing 25mph but that's another issue). My friend pointed to his bike mounted camera and the driver suddenly didn't feel the need to abuse us any more.
It must be exhausting to be so angry all the time, what do they think they gain from it?