I can't help it, but this is an endless source of frustration for me. In the seventies when you met another rider it was usually a raised fist biker salute, and everyone did it, everyone, or else they only had one arm. 
Nowadays I don't try to fiqure it out anymore, must be doctors & lawyers that can't see past the end of their own noses.  
I was always raising the left arm/fist salute of "Two-Wheel power club" as taught to me by other riders running by me back in the 70's when I started riding and it was like a kinship/wave thing.. I think I should start initiating more waves to many other motorists now myself after reading this thread !  I guess I should look at it as being a "two wheel goodwill ambassador" to let folks know being on a motorcycle is good Karma or something,it sure can't hurt  

Great thread and very educational  

 Keep it up !