muchcommonsense, This is straight from the New York DMV website:
“a horn is used as a warning to others. It should not be used unnecessarily or to express your anger at other drivers or pedestrians.”
“Road rage can include: Verbal provocations, such as yelling, cursing, excessive horn honking, rude or obscene gestures and threats.”
You can print this out in big colorful letters (the rules stated above) and place them on all the cars causing all that ruckus, or hand it to the drivers (if possible) or paste them up all over town. Or your best bet would be to take down these people’s license plate numbers and file complaints, because they wont stop on request by a civilian.