My dresscode, be it work or play, is jeans and a t-shirt/short sleeve button-up. While it's not at all sloppy, it's also not formal. My reasoning is that wearing a suit onboard (and I've done this plenty of times) is uncomfortable, so I choose comfort over looks. It's worked so far and the only people to give me cross looks when I'm sitting in F probably should take a look at themselves first.
