The cliche about New York City is that the amount of time spent in transit means New Yorkers do in public things suburbanites might keep locked behind French doors. Like breaking up with your girlfriend, or cleaning your shoes with your tongue.
What's more impressive, this man's frantic licking of his sandals, or the guy in the green coat just casually sitting next to him like this is the fifth shoe-licker he's seen today? He's probably just relieved he didn't find himself on a train with the Naked Racist Ranter. When riding the New York subway, it's all about finding the train with the most free seats and the least-threatening spectacle.