If they are coming up behind me and pop the horn, I assume they are just letting me know they are there and I give them a "thank you" wave. The things that motorists do that amuse me the most are when they have to get on the gas and damn near drop their transmission trying to pass me. Now, what pisses me off is the motorcyclists on crotchrockets that want to wind it out as they pass me. But I get amusment out of making vroom vroom noises when I see them at the next gas station up the road fueling up.