I've got an idea.
Why not have an inflatable dunces hat that pops out the top of a car when the driver's driving like an arse?
It must be pretty easy to electronically detect when someone's being a complete knob on the road. You could use sensors to detect when they've cut someone up, or when they've driven past you on the motorway at 130 MPH only for you to catch them up at the back end of a traffic jam 20 miles later.
Or when they don't indicate (you know who you are!). Or when they sit in the middle lane of a 3 lane motorway when there's no traffic in front of them for as far as the eye can see (but 3,000 cars approaching in their mirror).
The system could operate on a timer. If, say, you've just pulled out in front of someone without indicating, the Electronic Dunces Hat (EDH) would stay inflated for, say, half an hour. If your car detects you driving 6 inches from the car in front, even though it's clear there's 10 miles of traffic jams ahead of the car in front of you, it'd stay inflated for an hour.
Driving a BMW would, of course, result in the EDH being permanently inflated.
I really think this would work. There aren't enough police around to detect all the plonkers on the road and, in a lot of cases, a few quid on a fine isn't going to stop people behaving badly on the roads anyway.
However, a massive EDH on top of their car, indicating to the world around them just how stupid and selfish they are and that they are to be avoided at all costs, might actually make them think before doing the deed.