Eliza Hittman makes movies about teenage sexual desire. Her first film, “It Felt Like Love,” was about a 14-year-old girl who wants to have sex but doesn’t really know how to go about it, and she ends up in a situation she can’t control. In her second feature “Beach Rats,” Hittman turns her camera on the boys. Frankie is an aimless teen going through a rough summer in Brooklyn. His father is dying of cancer. And though he spends his days hanging with friends, picking up girls at Coney Island and the beach, he cruises for men online.