But why are we calling this road rage? OP hasn't done anything to provoke, annoy, irritate, etc. The BMW'r is being a jerk, and there's not much more to it than that.
It's road rage. The guy is clearly in a rage, whether he was provoked or not. Most road rage isn't provoked, at least not intentionally. The car in front of you is driving "too slow"? Hang a foot off his rear bumper, blow the horn, pass too close, cut him off, brake check him. The guy wasn't doing anything wrong, he was just not speeding quite as much as the rager wanted to.