My old Subaru...
Back in the mid 80's, I drove a nice, little Subaru coupe with a standard transmission. It had a very forgiving gear box that would engage the back-up lights without actually being in reverse. Just throwing the shift all the way to the right and not pulling down to set in gear closed the switch.
All it took was a second of coasting while engaging the lights to make tailgaters back off, even at highway speeds.
I've also been known to adjust my mirrors to bounce hi-beams back at offending assholes.