My go-to is to look confused because that’s genuinely the reason most of the time, ex:

I was riding home in the bike lane minding my own business, when a black Toyota Highlander (big SUV) pulls up alongside me, windows rolled down, and a bunch of teenagers from the back yell: “Dickhead” at me.

I looked back at them genuinely confused because they went out of their way to not only insult some random person but also to do so with their windows rolled all the way down.

They giggled and sped off on their merry way, and my thought is, they’re probably stoned or driving under the influence.

The suggestions about non-confrontation are fantastic, but what you’re supposed to actually do is memorize faces, vehicle details, license plates, and cross streets

Their probations officer would probably not be too pleased to hear about a repeat DUI, but there’s no way of knowing what happens to people in such circumstances 🤷‍♂️