As someone that cycled to work nearly every day last year I can say 100% that there are arsehole cyclists and motorists.
I saw one cyclist nearly get hit by a car and proceeded to kick the driver mirror on the way past. Now you'd think fair enough, the car was turning around in an office junction on an industrial estate and didn't see the cyclist as he was making his reverse move back onto the main road (parked cars both sides)..... sounds like complete driver fault and partially is, however..... there is a designated cycle lane that would have had the cyclist off the road had he chosen to use it, it actually runs parallel with the main road and pavement and away from the danger, long story short, the car driver went after the cyclist, completely cornered him at a round about got out and a fight ensued. 2 others and myself broke it up who had seen the whole lot and all said the cyclist was in the wrong for not being in the cycle lane, not having the perception or vision to see the car turning and then kicking the mirror off.
The closest I came be being knocked off was a car over taking me on a 2 lane road to then fly across the front of me into a left hand turn, I was doing near on 20mph so another 5 seconds behind me wouldn't have hurt.
The most apologetic person I came across was a while back, I was in a cycle lane going down a big hill, at the bottom, queuing traffic. A car in the traffic decided to let another car on the other side of the road out and as he turned he went into the cycle lane, I had to brake hard but the lesson was to look for cars in opposite junctions in the future. The driver was massively apologetic but both agreed it wasn't really anyones fault and had a bit of a laugh with him about it.
The short of it is, if people left with plenty of time and not last minute they'd be in much less of a hurry and probably (god forbid) enjoy their commutes and be less stressed, making less mistakes and annoying less people