I have had somebody follow me aggressively (in a car) with seeming intent to main before and it is a terrifying experience. They pursued me at 70mph in a 30mph zone. It was my second day driving a manual transmission and I accidentally tapped my horn with an old Ford Explorer behind me (no cars in front) as I was trying to shift into first gear to turn left out of a lot. A man exited the SUV at a red light and I ran it, hauled my ass home. And that's the story of how I learned to throw it into first gear quickly.
When it's just you and the other car on the road, there's no way of proving what happened, you just have to hope there were witnesses, or god forbid you do get run off the road, that the accident scene has enough evidence to show criminal intent.
Honestly, those examples are great reasons why I would support some kind of form of publicly shaming those drivers (via some kind of www.thisiswhycyclistsdie.net blog): Get cyclists to be diligent and record their rides and post the obvious asshole drivers and their plates.
Yes, there's probably giant privacy implications there, but fuck it. They're trying to kill people out there.
When it's just you and the other car on the road, there's no way of proving what happened, you just have to hope there were witnesses, or god forbid you do get run off the road, that the accident scene has enough evidence to show criminal intent.