I agree, if passengers are quietly talking to eachother during the demo without causing any noise, then you can't do anything, it's their perogative, same goes for someone sitting in an exit row, if they're sleeping i would leave them. Different story though if they were sleeping when i went to do the overwing exit briefing, i would wake them up quick smart.
Another thing with absolutely nothing to do with the thread, but i read something about it earlier. I cannot stand crew that walk through the cabin with coffee or tea and all they do is like robots walk through going, "coffee, coffee, coffee, coffee" or " tea, tea, tea, tea", it sounds terrible, especially if you're the F/A infront of them with the other pot of whatever, show some enthusiasm. I would get bored just saying that all the time, i have to change it around every time i say it just to amuse myself!
Oz