8. John Mayer
Katy Perry is the latest celebrity to join the long list of ladies on whom John Mayer has allegedly cheated. Rumor has it the singer's legendary wandering eye has led him to step out on Perry, Taylor Swift and even Jennifer Aniston. {relatedarticles}While there have been no official confirmations, it has been suggested that Swift even penned a song – “Dear John” – about his behavior and their subsequent breakup.