Smashing through someone's rear window.

Don't think he can sue for personal injury unless a permanent injury is sustained. This can only be judged 18 months after the incident and has to be permanent to at least 10% of the body. I'm no Solicitor so the finer details I don't know but one of my best mates (who was seriously injured by another's fault recently) has just been through all that. Even with a broken nose, collar bone, cheek bone and requiring plastic surgery to fix his face (that will never be 100%) he has got no legal avenues to pursue. This isn't the USA after all.

Best he could do is get a copy of the Police report and tell the insurance company to jamb it.

Happy to be proven wrong though. Someone needs to teach dick drivers a lesson or two - good luck to him, but I have my doubts.

Tell the insurance company to **** off, and you'll see them in court.
Don't bother with a lawyer, that's their threat they can bankrupt you with their lawyers. Tell them "knock yourself out buddy I'm going for free".

You think the judge will award costs against you to a insurance company?

You think the judge needs a smart arse lawyer to help see the situation and make a decision? He'll most likely be annoyed as hell that some ****** is wasting his time on trivial ****. It s a car window for christ sake, a lawyer costs $500 an hour and 2000+ /day to go to court. Everyone need to do a reality check.
Answer their letters, play the game, waste time, waste their money, , go to court for free It's your right as a citizen.:D