Was it a 4 way stop? Anyway this is nothing new. Back when I was in my 20's a LONG time ago (the 70's). I was screaming down a hill when a lady accelerated past me, slammed on her brakes and turned right into me. When they were loading me into the ambulance and I was coming back to concienceness she had to be pulled off me screaming "didn't you see my turn signal" and "you better pay for the damage to my car."
I believe this stems from the attitude (brainwashing) by the automobile industry and others that cars and their owners are entitled to the sole use of the road. Remember, when cars were first introduced on the public streets they were a hazard, routinely plowing down pedestrians, so the term "J" walking was invented by the car industry and promptly introduced to blame the walkers, not the cars. Quickly that took root and horses, pedestrians and bikes became second class citizens for road use with the public's love for the car. It just continues today.
Thats why I try to be a good ambassador on my bike and smile and wave a lot as, unfortunately I've seen too many rude, cyclists too. I no longer ride with some groups as they seem to intentionaly want to p*** off drivers, riding 3 4 abreats on two lane road not moving over when safe to do so because "I'm entitled to the road too" although true, not too smart IMHO. No easy answers.....