Rather than escalate what could be a case of road-rage, I recommend turning your hazards on. That's pretty much guaranteed to diffuse the situation. When people see hazard lights, they assume something is wrong with the car and pass without question.
If I'm on a multi-lane road, I don't change my driving at all. I've had people tail-gate me for several miles, timing every light so that we end up passing the people that passed us, only to have them eventually zoom around me and, inevitably, slam on their brakes when the light changes. They won't learn even when they see it first hand.
If I'm on road with one lane in either direction and I see a car approaching quickly, I turn on my hazards and pull off toward the shoulder before they even get close. They immediately pass without slowing down or tail-gating me.
I've also considered a sign that reads: "Slow Moving Vehicle" or similar, but my aim is only to encourage them to pass asap. A sign would only be distracting.
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