Choose a double breasted blazer and a navy crew-neck t-shirt to put together a dressy, but not too dressy menswear style. A cool pair of white canvas derby shoes is the most effective way to add a confident kick to the look. Clearly, it's easier to work through a roasting hot summertime afternoon in a easy and breezy outfit like this one. No doubt, a fail-safe option if we're talking dressing ideas for 40-year-old men.