If you drive in rush hour you see it all the time.
Somebody does something minor to the other that he doesnt like, an inconsiderate lane change etc..
The person then takes offence to this, and takes revenge by trying to do something to them back. Other person doesnt like this either and responds back.
Each time it escalates into something more and more dangerous until the only thing left is either to crash into them, or just stop in front of them and get out of the car.
We've only seen half that process in the video.
I'm inclined to disagree.
The Van Driver is clearly a nut job.
That aside, I've seen people do similarly stupid moves with no previous altercation between them. Infact just look at some of the other cycling videos on YouTube and you can see where there are other nutters who have done something totally stupid that's nearly hurt a cyclist with nothing going on between them beforehand.
I genuinely believe that nothing has gone on beforehand and the driver isn't on some kind of revenge mission to get him.