On my KLR:
"What is that, some kind of big dirt bike?"
(Actually had a guy at work tell me this) "Hey, something is up with your bike, sounds like it's only running on one cylinder."
But my all time favorite was years ago, on my little Ex500. Decked out in full gear, with my long wavy hair tied up and reaching almost to the seat, a carload of little douchebags in an Integra roll up next to me and the driver rolls down his window and says "hey babe, nice bike". To which I flip the front of my modular helmet up, showing my bearded craggy and very un-female face and say "Thanks!"