A grim portent of the twee revival: Bill Murray is being spontaneously cheeky again. Murray was spotted by fans, video creator Nicolas Heller, and “Page Six†in Washington Square Park on Wednesday afternoon. He joined cellist Jan Vogler, violinist Mira Wang, and pianist Vanessa Perez in renditions of “It Ain’t Necessarily So,†Lawrence Ferlinghetti’s poem “Dog,†and “I Feel Pretty†from West Side Story. Rachel Zegler is shaking. Conspicuously present for the show were the producers of a concert doc about Mr. Murray, New Worlds, which shows Ghostbustin’-Ass Murray performing at the Acropolis in Athens. The scene (which includes housewife Carole Radziwill) was broken up by the fuzz. “The cops say we have to turn off the microphones,†Murray said. “Let’s rip this place apart!â€