Sting pranced in a hoop skirt. Kevin Kline was mistaken for Calvin Klein. Liam Neeson forgot his first line—which was "I am Liam Neeson." It's all part of the giggles in The Play What I Wrote, a British import that opened on Broadway last month. Stars Sean Foley, 38, and Hamish McColl, 41, subject each night's surprise guest star to indignities galore. Director Kenneth Branagh allots guests only two rehearsals. "It's like the actor's nightmare, where you're waking up on a stage and doing lines you don't know," says Nathan Lane, but "it's the most fun anyone can have."