I took a flight last year between BCN and MAN, unfortunately I was sitting in front of a group of loud drunken shouting idiots. Despite the seatbelt signs being illuminated (was turbulent) they got up, stood around in the aisle, went to the toliet etc as they wished. The CC didn't do anything, mainly because two of them were stood there talking to them for half the flight. If pax see the crew obviously not give a hoot for the seatbelt sign, even when it actually is turbulent, it's hardly surprising passengers don't.