They say imitation is the sincerest form of flattery. But what happens when someone takes a song that you wrote, recorded and had a huge hit with . . . and just takes you to school on it? That's exactly what has happened to Taylor Swift, courtesy of fellow pop diva Jessie J, who just tore into Taylor's smash "I Knew You Were Trouble" during a recent live performance on BBC Radio 1's Live Lounge. This is a ridiculous master class in singing and Jessie completely reinvents Taylor's hit song. This chick rocks!