Who knew The Boss was into ballet? Bruce Springsteen dropped in for a performance of “The Nutcracker” with his two kids at the New York City Ballet last week. A spy reports, “He was dressed in all black with a diamond stud in his left ear and took the center seats in Row 5. He seemed enthralled and applauded at the right moments. As he left after the curtain, I shook his hand and told him, ‘I love you, man.’ He was polite and friendly.”