Why do motorcycle riders wave at each other?
As a rider for over 20 years, I've waved at countless brothers and sisters of the road. Cruiser, cafe bike, crotch rocket, enduro ... if you're on 2 wheels (or even 3 - trikes count!) I'll wave. While I've ridden American iron my whole life - Harley-Davidson and Buell - I don't care what you're riding. If you're out of the cage (aka "car"), you're a kindred spirit.