It's happened again. Much of America has got their knickers in a twist over the half-time performance at the Super Bowl, that hallowed 12-minute slot that introduced us to the term "wardrobe malfunction" back in 2004, after Janet Jackson's right nipple made a surprise cameo. And after tame contributions from the likes of Tom Petty and The Rolling Stones in recent years, on Sunday "controversy" returned to America's biggest sporting event when MIA, the English-born singer and rapper, "flipped the bird" at the camera during her guest spot in Madonna's medley.