Buy one of those led licence plate things and have it say back the **** off unless you want my rear bumper in your grill. If the other driver rear ends you it is their fault for following to close. Note this is not the safest method, but the asshole would learn to not tailgait ya.

But I understand where you are coming from, not a day goes buy that I'm passing a line of cars going down the interstate and already doing 70+ mph in a 65 when some douchbag feels the need to ride my ass.