Yup. That, and tailing them.
Most people don’t mind a single light flash if they’re the culprit (it’s happened occasionally from carelessness to all of us, even those who try to not make it a habit).
And most people will gladly move if you simply want to speed faster. But if you’re flashing your lights at them going 85 in a 65, you’re the asshole.
And if you tail someone to the point of danger, expect to get brake checked. And if you flash your lights at them incessantly, expect them to do everything they can to piss you off, now on purpose. Many folks will make you go around me and then happily move.
In short: treat others like you’d like to be treated. Even if you want to go faster, a little bit of patience and restraint enables you to do that both faster and with less stress.
Good luck getting people to drive calmer though