I once got stuck on US-501 near Brookneal, Virginia, behind a truck that was hauling some sort of wood chips and its rear doors were not secured, so the chips were coming out of the truck almost like a blizzard. I should have just pulled off the road and waited 10 or 15 minutes before continuing, but I was stubborn and simply backed off a ways to try to minimize the annoyance.
I don't find farm tractors to be the most annoying because I will pass them over a double yellow line as long as I'm not on a blind curve or a hill. webny99 mentions tractors being driven on the shoulder, but there's not always a shoulder available. I once got stuck behind one
in this general area east of Charlottesville and I couldn't really pass over the double yellow because I was perhaps fifth on line behind the tractor. Its driver was waving people to pass when he could see it was clear, but at least one driver wasn't willing to do it, presumably because of the double yellow line. The fact that I was starting to have to take a massive leak just made it that much more annoying.