I think it's really inconsiderate when people drive up to somebody's house and -- instead of getting out and knocking on the door -- honk their horn repeatedly. Car horns are loud and they signify warning or danger, and it's not like it's difficult or unhealthy to go for a little walk now and then...like, a walk to the front door.
You wouldn't drive up to somebody's house, roll down the car window, and scream "HAAAAARYYYY! I'M HEEEEEERE!" Would you? Say you wouldn't.
I am willing to accept horn-honking when it's raining terribly, but not under any other circumstances.
Somewhat related: it's also annoying when people program their cars to honk when they lock the doors. Again, car horns are very loud, and when you hear them that means something bad is happening. When I walk past a car that suddenly honks I pretty much jump out of my skin.
Respect for others, people! A little less noise!