Not too stiff. Not too floppy. No weird detailing. And nothing that looks like you've joined a country band. These are the key criteria for finding your dream denim shirt.
It's not always easy. But when you find it (we speak from experience), you'll start planning outfits around it. Why? Because it makes you look like you might own a record player and definitely read French Vogue (in French, of course).
Button it up and tuck it in. That's the office look done. Leave it open and roll the sleeves. It's off to band rehearsals. And most crucially of all, it goes with everything.