On my way back from ICN recently in WT+ the lady in front of me just leant over and slammed my window down without asking about a couple of hours into the (daytime) flight. I of course asked her what she thought she was doing and if it was affecting her and she said it was too bright. I then proceeded to tell her it would be manners to ask at which point she mumbled something in a foreign language. Natural light is better for reading which I was doing at the time.

I put the blind back up. Who did she think she was!!! I said to her to wear eyeshades if she wanted total darkness. Stez who was my seat partner looked a bit stunned as well. One window open did not appear to have any impact on the flight and so I am in the camp of if you want darkness put eyeshades on however if I could see it was shining in someone's eyes/IFE etc I would close it.