Simple advice, Don't flip cars off. Would you flip off someone pointing a gun at you? It's the same thing.

I am not saying the car is in the right, I'm saying don't play russian roulette.

Your friend is an idiot.

Any moron who is going to buzz a cyclist is certainly going to stop in the middle of the road if you give him the finger.

At the point the finger makes an appearance, you become the asshat.

I would be surprised if the police did anything even if you reported the driver. Did the driver actually break the law? Even if they did police are unlikely to act unless there is an accident or injury. Unfortunately "close calls" don't warrant police action.

And like the other guys said, you're on a bicycle against an angry driver in a ton of metal, it's best to keep your mouth shut even if it's not fair. Nothing good is going to come from pissing off an angry motorist when you're on a bike.

Your friend made a mistake: he tried to outasshole an asshole. He can't. You deal with an asshole by making sure they suffer consequences for their behavior. In this case that would have been a license plate number and a complaint to the police.

Well, on the other side, the finger will flush out those who should be reported (intent to harm).

If they are just oblivious, they won't even notice the finger, as they wouldn't check their rear view mirror for your reaction.

Flip away, just be prepared to record, dial 911 and/or fight (alu frame pump!)

I' d say call police and report him as a possible DUI. IMO, anyone acting that irrational must be under the influence and should be stopped and interviewed by the police.

So, contrary to what most people have posted above, my understanding is that in many (most?) states, what the guy did was likely a criminal offense, typically called harassment, or menacing, depending on how bad it was. You can report it as a crime, with the license plate number and a description of the guy, and the police may try to talk you out of it, but they MUST take your report if you insist on filing it. You do have two witnesses so that's helpful. The police may or may not investigate it, but it will show up in their crime records and if other people report the same guy or, god forbid, he actually injures someone, your report will help do something about it.

In many jurisdictions (this actually varies by state/county) there is also separate recourse in the form of civil penalties. I.e., you can sue him for either treble damages (which is likely low here) or some set number (say, $1000), whichever is greater.

Obviously, both of these require some effort on your part. I think we all should at least report interactions like this as a crime. It doesn't take much effort, and I think it could help in the long run. Getting a conviction or winning a judgement against him would require much greater effort obviously, and it also requires you to prove that he intended to do it. It seems he buzzed you both separately, and then was aggressive afterward, so I bet you could make some headway there. His lawyer will tell him to say that he didn't realize he was so close to you, and that his hostility was purely in response to your friend giving him the finger. That story is somewhat belied by the fact that he buzzed both of you separately, and was attentive enough to know your friend gave him the finger. I.e., he clearly wasn't just absent-mindedly buzzing you. Anyway, you get the idea. Here's an example of a successful lawsuit: http://www.velonews.com/...ought-justice_437651

Bottom line is most people in your situation would do nothing about it because of the effort involved, but I'd urge you to at least report it. Keep in mind this guy probably does this all the time.