In my experience much of the horn blowing is done by cabs. These guys are under a lot of pressure. They can work a 12 hour shift and end up owing money. If not cabs, it is someone else doing business, like delivery trucks. They will honk at other trucks double parking, then do exactly the same themselves. I’m glad I don’t have to do that.
Perhaps the most annoying source of honking is at a traffic light. As soon as the light turns green, someone will honk.