Someone was asking this question a while ago.
Here are some reasons why they and BMW drivers do not wave.
Top Ten Reasons Why Harley Riders Don't Wave Back:
10. Afraid it will invalidate warranty.
9. Too much leather and studs make it too hard to raise arm.
8. Refuses to wave to anyone whose bike is already paid for.
7. Afraid to let go of handgrip because it might vibrate off.
6. Rushing wind would blow scabs off the new tattoos.
5. Still angry from taking out second mortgage to pay luxury tax on new Harley.
4. Just discovered the fine print in owner's manual and realized HD is partially owned by Japanese motto manufacturers.
3. Can't tell if other riders are waving or just reaching to cover their ears like everyone else.
2. Remembers the last time a Harley rider waved back, he impaled his hand on spiked helmet.
1. They're jealous that after spending $30,000, they still don't own a BMW K1200LT
Top Ten Reasons Why BMW Riders Don't Wave Back
10. Wasn't sure whether other rider was waving or making an obscene gesture.
9. Afraid might get frostbite if hand is removed from heated grip.
8. Has arthritis and the past 900 mile ride has made it difficult to raise arm.
7. Reflection from $8000 worth of approaching bolt-on chrome momentarily blinded him..
6. The espresso machine just finished brewing.
5. Was actually asleep when other rider waved.
4. Was in a three-way conference call with stock broker and BMW accessories dealer to buy BMW chrome pegs.
3. Was distracted by odd shaped blip on radar screen.
2. Was simultaneously adjusting the windshield height, programmable CD player, seat temperature and satellite navigation system.
1. Couldn't find the "auto wave back" button on dashboard.