I don't know guys. I think there is plenty of ass-hole-ish-ness to go around on both sides here.
It's too easy to say the truck was the sole culprit. Yes, of course, there's no way in hell he should have ever intentionally pulled in to the bike the way he did. Watch the video though. At about the 21 second mark it looks to me like that rider either hits or kicks the truck before the truck cuts in to him. So at least some initial provocation came from the bike.
Definitely, bitch slapping someone's fender does not then accord them free rein to run your ass over. However, if you don't provoke to begin with the response may not come your way. It goes back to the old golden rule we should all be smart enough to know by now:
When you're on a bike don't fight with a car.
If the bike thought there wasn't room to get through he should have fallen back.
If the bike thought the truck was taking up more lane his way than he should have the bike should have fallen back.
The rider should have never reached out to hit or kick at what appears to be about the driver's door. Deserved or not it's just poor tactics and it's stupid. When you're stupid first someone may just turn out to even stupider (and bigger than you) in return.