I voted "leave it be," but this is the new me.
I suppose it would depend on the severity of the buzz. The kicks I've administered to side panels usually are payback for simple inattention.
The one time that I was actually run at — by a cab with a fare in the back seat! — I roared after him. I caught up to him. (New York traffic; no car car can outrun a determined cyclist.) We engaged in this weird scene that was like the O.J. white Bronco chase. I pulled in front of him, and he slowed way down, driving at parade speed. I did too. Cars on either side of us rolled past, wondering what the hell was going on in the middle lane. I think he was trying not to let me see his license plate or something. But I did. And I was fully prepared to call the Taxi Commission and report him. For some reason, I didn't. I can't explain it. It didn't feel right.