With most airlines out there the rules would be laid down in the uniform standards booklet. I can safely say that on board the aircraft it is down to the interpretation of the senior crew member on the day.
We all go by the letter of the law when it comes to safety. Thats our primary function and rightly so..... Jackets on or off? Is it really that big a deal?
Some people feel the cold more than others. We are all adults. Do the pax really mind? I think they worry more about what comes on their tray and what the movie is gong to be!!!