Denim jackets have been around for over century, so no need to question their relevance in your wardrobe. They're also more versatile than you think. You can wear them over top of hoodies, or underneath your raincoat as a layer on rainy days. Got a 9-5? Fight against "the man" by slipping a slim denim jacket on underneath a blazer, or heck, wear it as a blazer with slim (read: non-denim) trousers, an oxford shirt, and a tie.