History: These two seemed pretty cool with each other, up until recently. It all started with Taylor Swift's Rolling Stone interview in September 2014, where she referred to another female artist as her "straight-up enemy" while talking about her song, "Bad Blood." Many thought the quote was about Katy, since she tried to steal a few dancers from Taylor at one point. Then, Katy's subtle but shady tweet, which said, "Watch out for the Regina George in sheep's clothing," all but confirmed it.