Music, dancing, alcohol and tiny swimsuits — spring vacation in the United States, popularly known as “spring break,” brings thousands of young people to south Florida every year for a few days of uncontrolled fun, much to the chagrin of residents in cities like Miami Beach. At dusk on a gray Thursday, an unusual occurrence in Miami, going-out hub Ocean Drive has become an open-air club. Cafe terraces are packed to the gills, and the party is on in front of every art deco building along the promenade. The air reeks of marijuana. A car pulls up and blocks traffic. A young woman jumps out and b…