Re:
I don't think it is confined just to cyclists.
I recently took to riding motorcycles again and was stunned to have cars move to the right in an effort to block me from overtaking. Of course when I do inevitably overtake on my noisy, rusty ex army 500cc Armstrong with nice big steel pannier frames they can't wait to get out of my way, just in case I (will happily) take a layer of paint off their shiny car.
The difference is that on bicycle we are moving slow enough for the frustration that comes from believing you possess the road you are using to be expressed verbally and with the car horn.
I mostly cycle as far from cars as I can get or at least on the quietest roads I can find, but there are times when I inevitably have to filter through stationary traffic and ohh what fun that is. People in traffic jams really, REALLY hate being overtaken by cyclist and I guess they just retain that pent up frustration.... sad b'stards.