If they were in front of me, I would either slam on the brakes (squeal 'em as loud as possible, maybe they'll get distracted and drive off the road *hahaha!*), turn around, and punch it!
Or, if you are like me, you have a red spotlight, 100,000 candlewatt spotlight, and this in your car....
Retrieve the weapon of your choice and scare them back!
I have all blue LED interior lights too, so I'd probably turn those on too.