You can look casually dapper without exerting much effort by wearing a navy short sleeve shirt and a black crew-neck t-shirt. If not sure as to the footwear, complete this outfit with black canvas slip-on sneakers. When you have one of those dreary fall days, sometimes only a killer ensemble like this one can get you to face the outside world. And if we're talking casual dressing ideas for 30-something gents, this outfit looks good on most gents.