As a man of summer, you know some things. You know that flip-flops are not meant for the city. You know that shorts are, but they better be good ones. You know your swim trunks can be a little bit shorter this year and that they pair well with a floral shirt. The traditional rules of menswear are bending and sandals are next up for your consideration. Those flat, leather-strapped sandals you see women wearing right now are on trend for you, too. And, yes, that does include Birkenstocks.