Went out for a short ride a couple of weeks ago on a route I use quite commonly. While approaching a bit of a bump in the road I drifted out in to the lane to let the car well to my rear see me and then pulled back to the side and went over the hill. As the driver went by, giving me plenty of room, I waved as I usually do. He pulled over and I rode up thinking that it was someone I knew. It wasn't. He wanted to know if I had just flipped him off. After a moment of confusion I explained what I had done and noted that I always wave. He then spent a couple of minutes venting about a negative experience he had recently had with some bikers. I might point out that I would have been upset as well. However, we parted on polite terms.
What I find disquieting is the fact that I no longer feel comfortable waving at people passing me by, at least those coming up from behind me. It offends the midwesterner in me.