One of Taylor's favorites off her latest album Red, the track I Knew You Were Trouble features Swift's first ever dubstep inspired breakdown. There has been a lot of speculation over which of Swift's ex's is the subject of the latest breakup anthem but the majority seem to have settled on John Mayer. The lyrics do seem to allude to those of Swift's other song about Mayer, Dear John. (And I'll look back and regret how I ignored when they said run as fast as you can.) Swift explained the song is about "kind of being frustrated with yourself because you have your heart broken and you knew when you first saw that person you saw all these red flags and you just went for it anyway." Sounds a lot like her controversial relationship with Mayer. The lyrics, A new notch in your belt is all I'll ever be/ And now I see, now I see, now I see/ He was long gone when he met me/And I realize the joke is on me, also seem to allude to the musician who has a notorious playboy rep.
* We also consider Joe Jonas a potential subject due to the opening line, Once upon a time, a phrase which Swift also used in Forever and Always. She also states that the perpetrator was "a few mistakes ago" which could open up the time frame to include a relationship even as far back as Joe.