The Answer to the Question that was never asked
You get a white piece of silk fabric (I like silk here) about 3' x 2' and on it you silk screen in huge black letters.
You affix it to the bottom of the rear window sunshade and at the top while its deployed (up).
Your default position is to have the sunshade down. When and only when you have passed the offending person, do you employ your message for them to remember you by. All by the push of a button accessable without really taking your eyes off the road.
You heard it here first.
Because; whats behind me doesnt matter.