4. Katy Perry
It is known the Taylor Swift long-standing feud with Katy Perry was portrayed in her music video “Bad Blood”. Both musicians started out as friends. In 2009 Taylor got into a relationship with John Mayer and broke up, then 2 years later Katy Perry gets involved with John Mayer. This apparently started the feud. The feud was intensified when Taylor swift hired some back up dancers that were actually loyal to Katy Perry and when Katy called them back, they immediately left Taylor.