Wear your collar down; except when…
One of the things I’ve seen so many times here in the Netherlands is that many people are wearing their collars up, especially in summer. They do it with polos, shirts, and coats. A collar should be worn down; there’s no reason to point them up.
When should you actually wear your collar up?
When the weather calls for it, then you can pull up your collar to protect yourself from the weather. Simple.