Jen flexed her cougar muscles when she briefly tied down Hollywood's biggest bad boy, John Mayer, for about a year from spring 2008 till 2009. He even accompanied her to the 2009 Oscars. When they split, she joined one of the longest lists of A-list conquests in Hollywood history. Ouch! But we bet it was super-fun dating John -- who's almost 10 years her junior -- while it lasted.