Harley riders can't wave, it voids their warranty.
If you ever want to get into an argument with the Harley boys just point out the fact that when two of them are stopped idling at a light that together they both sound like an old air cooled Volkswagen.
But they still wave back more than MOST Beemer riders. But the friedliest riders are Goldwingers. Heck they even wave at motor scooter/mopeders.