Do you have a mirror? Here is what I do: With my mirror I know when cars are coming up behind me. On the troublesome bit of country two-lane (no shoulder) on my commute, I ride right tire track, maybe a little to the left of it. When a car comes up behind me, I slide right about a foot- an invitation to pass, but they still have to change lanes to do it. If there is oncoming traffic, I instead hold my position and hold my left arm out and down with palm facing back which pretty clearly communicates "do not pass." As soon as the oncoming traffic is done, I slide right and invite a pass. Part of the deal with frustrated drivers is that they don't know what to expect out of a cyclist. Even if they can't pass right away, they seem to be okay with me taking control as long as I communicate. The deal is, if they are frustrated behind me, when I pull to the right and wave them around, my cooperative gesture (waving them around to pass) seems to take all the steam out of their frustration.

Now, if they're already behind me and honking, that's different. But using this method I've managed to so far avoid such an encounter.