I propose that the car horn's functionality be split among two distinct noises. On the one hand, there would be the Happy Horn. It would make a cheerful, major-triad sound, one reminiscent of floppy-eared puppies and the Hallelujah Chorus. Parents picking their kids up at school would use the Happy Horn. The Happy Horn would be a gentle touch pad with a smiley face on it, or maybe a flower.
And then there would be the Angry Horn. The Angry Horn wouldn't respond to light touches. You'd have to pound it to make it go off, but when it did sound, Katie bar the door. I'm thinking of foghorns, machine-guns, and rampaging elephants. Imagine the sonic equivalent of Mike Tyson and there you go.