What do I do? I use the 115 db horn if someone doesn't see me.
I then back off and let them think about what they did, no need to rub it in.
If they seem unrepentant, then I give them a head shake and find a better route.
Basically, I treat them as though they are drunk or an eight year old who doesn't know any better.
The conclusion that I came to, is mostly because of the the editing and the video title.
It starts off with the car halfway into the ditch, so either he was trying to move into the lane from the right, or moved over when the bike came in from the left. I lean to the latter interpretation, from the editing & title (Someone was trying to prove a point). But it could be different. In any case the bike and car both want to occupy the same space. To me that usually signifies that the car was there first. The car driver then realizes which of the two vehicles is bigger, and a size of appendage contest ensues.
I don't have time or energy to deal with drunks or eight year olds who don't know any better. If you ride the way that you describe, i.e. without understanding that you could seriously hurt or kill someone, then I would treat you as a drunk or eight year old as well, and not want to be anywhere near you on the road. The problem is that people have to be sixteen to get a license, and drinking and driving is prohibited, so no one has any excuse anymore for that type of behaviour on the road. It's not a game.