When I drive my muscle car I just floor it. Since my rings are shot, I leave a thick layer of oil all over his car/windshield. I almost got shot a couple of times, but the fun is there.
If I drive my regular car I indicate I'm about to slow down, and I leave room for the guy to pass.
When I drive my beatup 1985 F250, I signal a right turn and brake hard enought to scare the guy.
My girlfriend just keep ignoring the guy, and frankly, that's the best way.