People honk in tunnels over here because:
1. We're easily amused. Honking in tunnels creates an echo, and the reaction you get from hearing it is the same as hearing your phone voice. "What? It sounds like that? Hah!" It just doesn't sound the same as when you honk on the open road
2. Bark:Dog::Honk:L.A. Driver. While we deeply value our magical multicultural land, it's important that we have some sort of language that can bridge the gap between our many walks of life. Honking is the perfect glue to hold together our balsa wood bridge of universal communication.