I had a similar but more aggressive one-off incident, and luckily 2 witnesses volunteered themselves and I got a photo of the guy when he came out of his car and his car (with number plate).
The police are following this up and so far are being very professional about it (my statement was actually taken word for word and everything, poor guy seemed to have quite a sore hand after writing it all down though).
I would report him to the police, if possible see if there are other cyclists that have witnessed the same behaviour. Failing that, if he is working for a company rather than himself, report him to his boss.
If you do decide to contact him to have a word, be very careful what you say, i.e. say nothing that could be misconstrued as a threat.