Gosh, people do get worked up about their right to sleep on a late evening/night flight! I generally travel alone, and on a night flight I will almost certainly be trying to sleep, but if people in nearby seats are conversing at a slightly lower than normal daytime volume I would regard that as perfectly acceptable.

When I'm ready to sleep I will insert ear plugs, don eye shades, and to sleep I will hopefully go. If the nearby conversation is so loud that it percolates through my defences for more than a few minutes, I would try jamming the earplugs in further; if that didn't work, then I would probably ask the cabin crew to have a word. I certainly wouldn't sit/lie there cursing.