When Styles and his One Direction bandmates presented an award onstage, Swift, who was sitting with Selena Gomez, was filmed mouthing "shut the f--- up!" in the audience, reported Us magazine.
Swift, 23, previously mocked Styles by speaking in a British accent during her 'We Are Never Ever Getting Back Together' performance at the Grammy Awards in February 2013.
Later in the evening, the entertainer won big for her 'I Knew You Were Trouble' hit, which was reportedly inspired by her split with Jake Gyllenhaal.