in looking around at sites that may fit the bill for me, I found
this one, which allows for a privatized version of what SteveDallas was talking about -- in this case, a way for strangers to let you know how badly your teen/crazed spouse/addled parent is driving.
In addition to wanting a site where we can publicly shame AssholeDrivers, I am seriously thinking of purchasing one of those
scrolling message boards (complete with cigarette-lighter power adapter, of course) which would allow me to post such messages as:
"BACK OFF, ASSHOLE"
"CONGRATULATIONS, YOU WIN THE 'WORST FUCKING DRIVER OF THE DAY' AWARD"
and, my personal favorite,
"PULL OVER, GET OUT OF THE CAR SLOWLY WITH YOUR HANDS UP"