Tailgating is very dangerous... getting out of an angry person's way and taking down a plate number is your best bet. Hope that your revenge will be served cold. Making them angrier could just get you killed.
If they aren't being angry about it, maybe they just don't realize how dangerous it is. A few calm words at an intersection might be helpful. Most people don't want the hassle of finding a cyclist under their front bumper if they stop and think about it.
On the other hand, I'd sure be fantasizing about lobbing a handful of pebbles over my shoulder in the direction of anyone who was harassing me... then hopping on to an off-road shortcut.