[SpookyZalost]

...I've actually been looking into a trunk mounted directional microwave beam cannon...

Say what!?!? 

I've seriously considered a spotlight on the back to flash at drivers, especially those that leave their brights on behind you.

surprisingly easier than you might think, you can get the parts from an old microwave... just make sure it's fully discharged first... and only dismantle it if you have a nice big open space to do it in, in case you have to run... KABOOM lol.

but effectively it's like a very short range directional EMP, and completely hidden,  seriously what are they going to say, 'oh I was following too close and then he made my car turn off"? lol who would believe them?