On my ride last Sunday, I was on a three-lane road (a wide one at that), with almost no traffic, when a clown in a Taurus approached from behind. I was about 2 feet out into the road, and he laid on his horn from about 100 yards behind me all the way till he passed. I just smiled and waved at him, and I think that pissed him off even more, because he laid back on the horn again, even though he was already past me. So I smiled and waved again, as big as I could so he'd still see it.
Sometimes I'll flip them off, sometimes shout back, depending on my mood and the situation, but I always feel better when I manage to control those impulses and just wave at them instead. The morning before the above incident I was riding to my WW meeting, and my route takes me across the biggest major multi-lane road in the city. The light where I cross has detector loops in the pavement, but I can't get my aluminum bike to trip them. I guess I need to carry some ferrous material. Anyway, I can sit there forever before the light cycles, and this particular morning it was early enough that there was almost no cross-traffic so I crossed against the light. A car was approaching from my right, but it was easily 300 yards down the road. It didn't stop them from honking at me as I crossed their path, though. That was so completely unnecessary that I did a "get-away-from-me" kind of hand flip at them, which made me feel better, even though they were probably too far away to actually see it.