Well *that* startled me out of a year's growth...

Someone using their car horn when cut off in traffic? Expected. That car horn having been designed to simulate a train whistle including the volume thereof? Not expected at all.

Considering the reactions of the other drivers I'm surprised that it's legal and/or hasn't caused any accidents by now.

I was walking along the sidewalk right next to where that van was. My ears are still ringing.