I'm one of those get over in the right lane unless your passing someone. That said I went down to West Virginia this spring to pick up a yearling Icelandic horse. With horse on board and traveling on a 2 lane windy mountain road I'm doing 40 in a 50 mph zone. After having 1 car stuck behind me for maybe 5 minutes I finally came to a small uneven pull off but feeling sorry for the car I pulled in. At first I thought the passenger was giving me a thank-you wave and then saw it was a 1 finger salute. Still kinda ticks me off.
We always did our best to be as polite as possible but when we had the Endura towing a vehicle sometimes it was just impossible. We, too, were subjected to some very expressive (and not very polite!) sign language. We would just laugh it off and think the guy should lay off the caffeine.
Side note on the Icelandic horse: I don't want to cause thread drift but an Icelandic horse is the most amazingly comfortable to ride. While I am not grossly overweight (a bit fluffy, yes) my legs are short in comparison to my height/weight. That makes riding uncomfortable a lot of the time. Because the Icelandic horses are not huge and exceptionally strong they offer one of the best riding experiences imaginable.