There's a really good trick I use on tailgaters - and it seems to work every time...
When someone behind you is so close that you can't see their front numberplate, gently slow down WITHOUT applying the brakes. Drop a couple of gears with perfectly matched throttle - it takes practice, but it's worth it - so that the car doesn't give an almighty jerk. Sit like this for a couple of seconds, then absolutely floor it back up to the limit, or just slightly over, or under, depending on road conditions. Naturally the car behind will still be in too high a gear so have to frantically downchange to keep up the one-yard gap between your cars. After the third time they usually realise that they're too close and keep a respectable distance.
Another favourite of mine is when they come up far too close to you at the lights and you "accidentally" put it into reverse and drive back a couple of inches. Or stalling on purpose when the lights turn green then getting through on amber. I won't do it if there's a few cars behind me, but if it's a tailgater or some ignoramus in an SUV, hell yeah.