Horns are safety features. They are meant for avoiding an accident, not for venting frustration. Here in California at least, using your horn because you’re feeling impatient at a green light is illegal. (Granted, so is using your phone while stopped in traffic, but that doesn’t make you in the right for honking.)
When safety is involved, yes. Laws vary by state, and of course enforcement varies even more, but the law in California is quite clear; horns are explicitly not a general purpose signaling device.
not a californian, so I can't speak to the laws there, but I don't see anything wrong with a quick tap on the horn to let the person know they missed the light change. in my view, this is communication, not mere venting. I would never give someone the full blast unless they were actively doing something unsafe.
that said, people expect to go when the light turns green. violating people's expectations as always at least a little dangerous on the road. they should know better, but they don't.
I live in California now. From my experience people are quicker with the horn in bigger metro areas. There's always the one guy who has no patience - although I try to keep in mind that person might be justified in trying to get to a hospital or some other emergency.
But generally there is a progression to events which follows what one would expect when walking:
1- Polite "excuse me mis/sir/mam" - tap on the honk
2- Louder "EXCuse ME mis/sir/mam" - double tap/one a little louder
3- Very loud "EXCUSE ME PLEASE?" - loud honk
Inevitably, a significant percentage of the time I see this, the person that is being inconsiderate and blocking traffic/a doorway will be annoyed at the person trying to move around. I wonder if there is a study as to the percentage of the population that has this type of reaction.
Horn honking is like a language. I doubt very many people are leaning on their horn when the person ahead of them is taking too long to take off from a light. Usually this is communicated through short, almost staccato honks from the horn. To communicate "shit you're about to crash" people lay on the horn. I don't think the honks used to wake up people dozing off at a green like are being mistaken for safety honks.
