1. say unkind and possibly untrue things about their ancestry, their chromosome count, and their sexual habits
2. reach up and adjust the rear-view so as to bounce their high-beams right back in their eyes
The typical response is either to flick the high-beams off (hey, thanks!), immediately shift lanes while keeping the high beams on (if that's in my blind spot mirror now, guess where THAT gets aimed next, fuckhead?), or drop five or ten carlengths back... while keeping the high-beams on. Once I even got a REALLY special contestant with an older car who held the lo/hi toggle switch down manually, in order to light up BOTH sets of filaments for the ULTRA high-beam... which, of course, went right back in his/her own eyes courtesy of my rearview. Congrats, a winnar is yuo.
The response tonight was a new one, though. Suburban Mom actually followed me into a grocery store parking lot to berate me for how "unsafe" it was for me to shine her own brights back at her. Seriously. I boggled. Then I started laughing. Which pissed her off even more, as she couldn't figure out why I was laughing. Until I asked her how it was "safe" for her to shine those brights in not only my eyes, but those of every single oncoming car in traffic, but "unsafe" for me to shine those same lights right back at her.
"But... but... but... that's different!"