One time when I was driving to work, I was stopped waiting for a traffic light behind some other cars, and a guy in the opposite lane was waiting for a gap to turn onto a parking lot.
Traffic started moving, and I was about to go, but decided to stop and let the guy in first.
But from his perspective it looked for a second like I wasn’t stopping. And that single hand movement that went from “fuck you” finger to “thank you” wave made my day.