Something you definitely shouldn't do under any circumstances to tailgaters is turn on your rear fogs briefly to look like you're braking so they hit their brakes and laugh at their bewildered expression. You especially shouldn't do this multiple times until they get the message and drop back.
Tailgating is pointless and dangerous, pushing the driver in front may well force them to have an accident or make a mistake wrecking your car and theirs by harsh braking. You wont get where you're going much faster by driving like a cretin and a death could be on your conscience. I drive quite quickly but if I end up behind a slow vehicle I don't rush to overtake it, I just sit at their speed and let them drive comfortably because that actually makes them quicker (they'll be smoother and more consistent) and thus makes you quicker. Also most tailgaters cant drive, I got overtaken by one who then shot around a blind country bend on the wrong side of the road. Speed doesn't necessarily make you a good driver.
I sympathise however with those against people who hog the middle or outside lanes. Technically they are overtaking lanes so if someone is moving quicker than you then you should get out the way where safe to do so. As for people who try to push in at roundabouts, another thing you definitely shouldn't do is accelerate earlier than they do forcing them wide so they have to do a whole revelation to turn off.