I have just come back from holiday in Vietnam. I live in Korea so it was a 5-ish hour flight, left Vietnam at midnight and back around 5 Korea time. I was looking forward to a rest on the plane, didn't expect silence, but I had ear plugs so thought I'd be fine.
A group of 5 or 6 women sitting behind me talked and laughed at top volume the whole flight. I could hear them over my ear plugs, and even over the entertainment system once I gave up on the idea of sleep. The rest of the plane was pretty much silent. (Being loud on public transport is just not on in Korea, and grandmas will think nothing of shouting at you to shut up if you talk too loudly.)
Eventually, I turned round and asked them politely if they could be a little quieter. They just gawped at me, were quiet for a few minutes, then went back to talking loudly.
I get that they were travelling, probably excited to be arriving in a new country, but is it unreasonable to expect people to think that others may be tired/on their way to a day of work/wanting to sleep, especially on a flight at that time of night? And especially when travelling to a country where it's pretty well known that people are quiet in public?
For what it's worth, I always try to be quiet in public places, especially enclosed ones where people can't readily escape. I think it's just manners. But willing to accept that I'm wrong.