I've never experienced the "it's so loud I can't sleep" phenomenon, but I'm constantly surprised at how often I hear business people discussing sensitive trade secrets on flights, hotel restaurants, etc. I've often thought that if I was one of their competitors I'd now know exactly what they're planning and how much they've budgeted.

Rather than get into it with a passenger, my reaction would be to get up to go to the lav and have a word with the FA and ask them to resolve it.