Hey Bradley, like you, I can't stand those type of people. They are in such a hurry and that's how accidents happen. You know what they say, haste makes waste and there is no excuse for weaving in and out of traffic during commute/rush hour. It must have been fun to see his expression and when I was your age I did similar things. But having said that and even though it made you feel good, it may have been the wrong thing to do. Let me tell you why.
You said in your post that you were stopped at a light while Mr. Jerk was doing the weaving thing. So presumably, there was no immediate risk of an accident as traffic was at a standstill.
Horn laws in most states have not been changed since the 70's, and even when they were amended the laws were geared to reduce noise levels in urban areas. However, most state's laws (though rarely enforced) make it clear and read similar to this: "The driver of a motor vehicle shall when reasonably necessary to insure safe operation give audible warning with his horn but shall not otherwise use such horn when upon a highway."
I for one have been startled before at an overly loud horn that was used to "scold" another driver for his stupidity. Such a loud horn could have made another driver in the opposite direction over-react resulting in slamming on the brakes just to see where the warning was coming from and in itself, could have caused an accident.
In addition to that, there's the whole "Road Rage" thing where people out here have been known to get out of their vehicles to fight, even pull out a gun in response to an action from another driver.
Now, I'm not saying to be a "wus", only to use good judgement and "pick the fights your sure you can win".
Do I make any sense?