Around the Twin Cities (Minneapolis/St.Paul) you get a lot of people in SUVs not taking into account the size and maneuvering of trucks. I have seen a couple try to pass from 3 cars back when the truck has already signaled a lane change. Then they get mad at the truck (lots of honking, cussing, etc.). It is especially annoying when you see the "look for motorcycles / bikes" bumper sticker on the vehicle acting like an idiot.

You are so right about the headlight flash, help the truck driver quite a bit.