Once, while driving my (farmer) boss's 85 F250, I had someone decide to tailgate me without dimming the headlights. That truck had an adjustable spot light mounted through the A pillar. I just turned it around backwards and turned it on. That person backed off in a hurry.
This is my favorite one. Back in the early 90's, I had a 79 F150. Since I was about 20, I did go back home fairly often to visit and I always headed back to where I was living at about 4:30 Monday morning. There was a white S-10 (pretty new at the time) that would tailgate me with the high beams on at the same area every time. The driver would folow me for several miles before finally deciding to go around. The guy I bought the truck from built a 302 with a HUGE cam, had 33" tires on the back, and the truck had 2.75 (or so) gears. It was pretty useless for highway cruising at 55 MPH and had poor vacuum. This guy had also installed a "smoke screen". He rigged it up so that he could run a bottle of ATF into the intake and BOY would it smoke! I finally got tired of the S-10 tailgating me so I was ready for it to happen again. When it was right there in it's normal spot, I dropped the transmission out of drive and into second. Then I opened the smoke screen valve. When I saw a little smoke coming out or the side dump exhaust, I let off the throttle and watched the smoke roll. The S-10 decided to go around me pretty quick. Surprisingly enough (said sarcasticly), that solved the tailgating problem.
These days, Since I'm getting older, I just usually slow down when the tailgating at night starts. By the time I get from 65 down to 50 or so, they usually go around. Of course, I like to do a speed drop of at least 5MPH while we're going uphill with a double yellow line. There has been a time or two that I couldn't shake them at 45MPH so I've slowed down to 30MPH.