Hopefully these fashion faux pas are quite evident.
Polos & Shirts - Don't pop the collar on a polo shirt, button down shirt or rugby shirt. At no time, ever, ever, ever. A collared shirt should not have an erected collar, unless you are at a costume party or you have a nickname that starts with "The" and ends with "Situation". Keep the collars down and keep the compliments up.
Jacket - Sport coats & suit jackets should have the collars down, creating a sleek, slim look. Only in extreme weather should the collar be popped and only to keep yourself warm, not as a fashion statement. Otherwise you will look like your hanging with Crockett & Tubbs, which is no bueno. And please for the love of all that is stylish, do not push up the sleeves of your jacket. Don't even think about it, it's just wrong.
Overcoats & Trench coats - With as much passion as I beg and plead you keep the collars down on your shirts and polos, I beg and plead that you to keep the collars of your overcoats up. Overcoats & Trench coats are meant to have popped collars.
Peacoats - the naval Peacoat has to have the collar popped, it is the only proper way to wear the coat. Without the collar standing at attention, the jacket looks boring and quite mundane. Keep it cool and keep the collar popped at all times.