There's an urban legend that, if you see a car at night with their lights off and you flash your brights at them, you may be triggering a gang initiation where they will hunt you down and kill you.
It's the first thing I thought of when I heard the story of what happened to a young man who lived in our town. He was riding home with some friends, when an SUV came up behind them on the highway, tailgating them, and started flashing their brights. The driver flashed his brake lights at the SUV, at which point the SUV moved over to the right, pulled alongside, and fired shots into their car, fatally wounding the man.
I can't imagine what they must be going through. To have such a random and senseless act of violence inflicted on them, and then to know that the murderer is still out there; I know it makes me angry and scared just thinking about it, and I never met this young man.