When spring arrives in New York City, something special happens.

As warmer, drier weather sets in and the days get longer, outdoor dining returns, music fills the streets, and pedestrians find many more reasons to smile. New York is a happier, friendlier place in spring, and the increase in outdoor activity is the obvious sign.

But in a place that gets a reputation for having no joy or sense of humor, spontaneous outbursts of either (or both) are a much better glimpse into the…