I wave generally everytime, Unless I am too busy watching the road.
Or if I am in a real bad mood, I don't wave... but thats not very often.
But when I am in a bad mood if someone waved to me I guess I wouldnt be in such a bad mood any more and would wave back.:)
I think only once have I been waved first :confused:... generally it always a response to my initial wave.
And here is a wierd one, there is a yellow toyota hilux getting around that I get waves and wave to, and somehow even after I changed my vehicle three times I still get the same wave when ever I see him :S

