Mayer notoriously romanced Swift, who wrote "Dear John" about him, in 2010 and had and on-again, off-again relationship with Perry from 2012 to 2014. The claws came out in September 2014 when Swift revealed to Rolling Stone that her new song "Bad Blood" is about a rival female singer who is "very competitive." "For years, I was never sure if we were friends or not," Swift said. "[Then last year] she did something so horrible. I was like, 'Oh, we're just straight-up enemies.'" Perry stoked the fire with some Mean Girls shade.