Well maybe that idiot is just horny.
Anway, I'm not sure about horns, I don't see why we need them. Sure you can show your frustration, but you can also just wipe it off and keep driving. Usually if people use their horn on me, I get frustrated a little with them, I just don't see why you would bother. I only ever use my horn when I mess up some corner or something.
If I want to pass someone and I'm alot faster and they are blocking or whatever I usually use my lights... But this is useless seeing as no one uses their goddamn mirrors anyway...