Also, don't ever, ever tap your brake lights to get a tailgater to slow down in D.C. -- I did this once (standard Michigan practice)...
As it was a standard NJ practice when I was there.
Then I moved to Texas. Driving home from 6th Street one night on Mopac, I had some idjit zoom up behind me doing something like 95. I was in the left lane, and there was a car I'd just passed not too far back on the next lane over. I was probably doing 75-80 myself. Instead of pulling around to pass me on the right (there was plenty of room), this asshole tailgated me (I couldn't even see the reflection from his headlights, he was so close) for a short while. After tapping my brakes didn't do anything, I removed my foot from the accelerator and slowed it down to about 35 before he got fed up and zoomed around me.