Sorry, I don't think I have the right to flip off a cop in traffic or anyone else. It's one of several actions classified as road rage, illegal in many states. If you can't control yourself on the road I don't think you should be on the road. Driving is not a right.
I referred to a thought expressed in a
passive and harmless manner, which you choose to regard as
road rage. FYI, "road rage" is a sustained confrontation.
If the individual in this example had confronted the cop, face to face, denouncing him in an obtrusive or threatening manner,
then the cop would have been quite correct in arresting him and charging him with disorderly conduct. But that's not what happened. In this example the individual was driving by, moving away as it were, expressing a thought in a perfectly harmless, unobtrusive manner.
Rather than ignore it and brush it off as an example of wholly avoidable nonsense the cop chose to pursue the fellow and make something out of nothing -- and in doing so remove his protective presence from the area he is paid to protect for the sake of wrongfully avenging his bruised ego.
Whether or not you disapprove of that fellow's action, what the cop did is assaultively violate his, and
your, civil right to peaceful, harmless public expression.