I guess I'll start with the whole horn honking thing... Yeah, you can't just blast your horn to say hello to a buddy walking down the street in Massachusetts.
No person operating a motor vehicle shall sound a bell, horn or other device, nor in any manner operate such motor vehicle so as to make a harsh, objectionable or unreasonable noise...
Hopefully, you'll never need to use anything from this list but it's good to know just in case. Here are some scary driving scenarios and how to handle them.