People are people and not always nice people, whatever their mode of getting from A to B, people will be and act in accordance with a whole range of emotions and sense of "rightness" (as in they are in the right).
Walking (High winds heavy rain) to the school the other day with User76 to go to a function with Squidge was a warm fuzzy day, as there are large puddles all along the road next to the only path up to the school, every single motorist, tankers, trucks, vans & cars alike slowed down and moved round the puddles upon seeing me, I was a smilley happy waving noddy thank you-ing pedestrian. This was a lovely heart warming pootle to the school. I was glad we did not arrive drenched head to toe in muddy puddle water.
However, another time, every single motorist will go through the puddles on the school run making it look like all the parents and smaller children are having a mud wrestling after party in the playground. They are not small puddles and at speed they create a wall of water that literally soaks you head to toe.
Sometimes herd mentality kicks in, if one does it they all follow suit.
It should be noted that the oil & fuel tanker drivers from the depot in the village (in my experience) always slow and never drive through the puddles. They also give me lots of room when cycling, they slow right down keep far back not snort up my bum and overtake on the other side of the road.
I think in big cities there it is most likely a lot of stress and eek cycling or driving, I have driven through London once, it was quite an experience. I know there are some places where even in driving you can slow down, let people cross roads, let people out, all happy smiley and then their are some places where if you are "nice" and let someone out you will end up with eleventy millions cars taking advantage of that.
I think is is plain stupidity and dangerous in today's world to get into a confrontation with another traveler of any description, whether wheeled, motorised or pedestrian but I can also understand after a close pass or brush that the fight or flight might kick in and the red mist descends but you do not know all the time that it was deliberate, people are not perfect, mistakes happen, accidents happen, escalating a simple mistake into damaging things and blood being spilled deliberately a ridiculous stance to take as your default response.
I don't ride in the gutter and I am still a "learner" but I ride along, and make sure when I need to move out I peer lots behind me and then move out, I don't stay in the middle of the road unless I need to, I will pull off the road if I create a long queue of traffic cos I don't cycle very fast, I mostly cycle in a small area, I am very memorable and noticeable and I don't want to promote anger towards me out of frustration of drivers at getting stuck behind me at 5 mph. That said I am not a big city cyclist I am a small village and the bits in between them cyclist, albeit that the only road into the village is one of the busiest B roads in the country.
Share the road nicely, be nice to others and hope they will be nice back, if you try and tackle aggression with aggression the whole situation gets worse, I could be wrong but that is my two pennys for what it is worth.