I find that people respond more to a shake of the head than to the finger.
The finger makes people pissed. A shake of the head shows disappointment and usually makes 'em feel like a child doing something wrong.
In many cases they will flip you off if they see you shake your head. I do it all the time, lol. In fact, I sometimes make a small wager if someone is in the truck with me, lol.
I clock more driving miles than most people who
"don't drive for a Living". I do about 60,000 miles a year (I hope that will slow down now that I'm retired). I see my share of idiot drivers, I also understand that there is a very small chance of my ever encountering that idiot, again. I don't hold a grudge, and, in fact, I don't even give them much thought, I have far too many things to deal with, without adding some BS about what some driver did. He either screwed up, or he's a poor driver, as long as no one was hurt and there was no damage, it's over. Let it go.
That said, there have been times when I have phoned the police and given them the vicinity, a description of the car, and the license plate number, and a description of the driver if I could.
If a driver soes something stupid, and we have eye contact, I will usually just shake my head at him, and, at least one of two things will happen, usually both, He well either flip you off, or speed away, or both. Rare is the occasion when an offending driver apologies, either by mouthing an apology, or waving one.
Either way, if there was no physical incident, at that point, it's done, at least for me.