Am I being unreasonable in thinking that it is extremely poor form to flash your headlights as a way of indicating gratitude.
Especially if you have stupidly bright LED headlights, even when they are dimmed. Especially in the dark.
There are times when a little flash of your headlights is useful or necessary, like when you are indicating that you are allowing another car to pass, but shining a bright light in someone’s eyes is a really crap way of saying thank you.