We've all encountered our share of prickly, self-righteous cyclists with a beef against motorists, but in this case, the blame is with the guy behind the motor. The Audi driver drives into the cyclist's area of a road, and then punches a guy when he's called on it. And, of course, some other guy videoed it.
That guy in the Audi seems pretty tightly wound; sure, no one likes being yelled at, but that guy knows what he did and it sure wouldn't have killed him to not be a dick about it. Cyclists have all the protection of riding a hatrack, so having areas where 4,000 lb cars aren't allowed makes sense.
The lesson here: don't be a jerk and punch people when you're in the wrong. And, if you're a cyclist in this situation, don't forget the headbutt! You're wearing a helmet for a reason!