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 400 miles have made it difficult to raise arm .
7. Reflection from etched windshield momentarily blinded him.
6. The expresso machine just finished .
5. Was actually asleep when other rider waved .
4. Was in a three-way conference call with stock broker and accessories dealer .
3. Was distracted by odd shaped blip on radar screen.
2. Was simultaneously adjusting the air suspension, seat height, programmable CD player, seat temperature and satellite navigation system .
1. Couldn't find the "auto wave back" button on dashboard.