I tend to come up to those when they park, and tell them in a very calm note that I drive an 18 wheeler the some of the time for work (which I do), and that I will have in mind their kindness to me when I was on a bike. They seem to start apologizing pretty quickly. No threats or anything, but they seem not to like the idea that the cyclist they shouted at is a truck driver, trucks which are about ten times larger and heavier then their puny pick ups, it's actually funny to watch. Maybe they remember that they will have to share the same road with my truck when I'm working. Maybe it gets them worried a bit more then I worry about their pick ups when I'm on a bike.