It’s called Hupkonzert, and we have no English equivalent. The meaning is fantastic, and it’s perfect for the summer.
I bumped into this word while going through some recent German-to-English translations of other car terms, like how they have a significantly more ominous word for ‘blind spot’ than we do: death angle.
Anyway, they also have the lovely word Hupkonzert, which literally translates to ‘honk-concert.’
It refers to when a bunch of cars in traffic all start spontaneously honking. German Wikipedia (one of the best foreign-language wikipedias) says that the origin of the word comes from when people would all get into their cars for a wedding or after a soccer game and go on an impromptu parade, waving their relevant team or country flags out of the windows or sunroofs and honking to get more attention. The whole idea of these car parades has its own word, Autokorso, which just translates to car-parade, basically. That word is less exciting.
The honk-concert word, though is much more fun, and I do think it should extend to any and all spontaneous mass-honking that breaks out in traffic for whatever reason. I plan on driving around in rush hour gridlock, honking at random to try to get some of these concerts going in America. It’s gonna be a loud trend.