It's absolutely a thing. Sometimes people forget, and you can remind them by flashing your highbeams at them. However that's maybe one in fifty encounters in

It's absolutely a thing. Sometimes people forget, and you can remind them by flashing your highbeams at them. However that's maybe one in fifty encounters in my experience, most people remember most of the time. A lesser known trick is you can flash your highbeams before cresting a hill or going around a blind turn to warn drivers on the other side. I rarely encounter other drivers who do this, but when I do it almost always works.