I don't mind drivers yielding to me and waving me on if it's a fluid action that doesn't unnecessarily disrupt traffic flow . The deal with the guy putting on his flashers is a new one on me. That seems a bit much, unless he had a really good reason; particularly bad section of road, traffic, etc.
Strangely, one of the more difficult things I find myself dealing with, are the reflections on car windows. Often, I have a hard time seeing the driver inside the car well enough to know for sure what they're doing. Opaque tinted windows are the worst. That can kind of slow movement.