WIY – The question was about rebellious teens and was answered in that vein. So is the following: If the kid thinks he is invincible and is therefore not wearing a coat, how is butting heads with him going to make that go away? The point is, a child that age can monitor his own temperature. A parent telling a kid that age to put a coat on is telling him that he is not intelligent/responsible/trustworthy enough to make such a simple decision. That is how they hear your suggestion and that is destructive. They want to believe you have faith in them and trust their choices. If you want to risk giving bad messages over, I wouldn’t waste it on something like a coat.
If you see them making lousy choices about more important things, you still have to find a way to let them know EXPLICITLY that you love them, you know that they are old enough to make their own choices, but you are worried about some of the stuff they are doing. Or you are worried about some of the choices they are making. If you give that information over with a sense of responsibility and tell them that you know life is a struggle but that ultimately it is their choices to make you are not putting a stamp of approval on their poor choices. you will have less of a chance of making them feel small and burning bridges.