We'd love to suggest resort casual or at least grunge chic, but not everyone likes to dress up.
The Mexicans are usually the best dressed, but even they forego jacket and tie for a nice button-down and slacks. The most elegant restaurants, like Café des Artistes, simply request that men wear T-shirts with sleeves.
If you enjoy looking like a million bucks, don't despair: looking good is always in style. The maitre d' will take notice.