Vince Vaughn is coming down hard on Jennifer Aniston’s burgeoning new romance with musician John Mayer. The actor has reportedly advised his ex-girlfriend to break up with her new man, telling Jenn: “You can’t be serious — this guy is just using you to make a name for himself.”

A livid Jennifer hopped on the defensive, reminding her The Break-Up co-star that he is hardly in a position to tell her who she may and may not date: “She told Vince that in case he didn’t notice, John already had quite a name for himself … and if Vince didn’t like the reports that were surfacing, he should stop reading the papers and spare himself a heart attack!”

Jenn was left “highly amused by the whole conversation,” a spy for The National Enquirer reveals.

Jealous much, Vincie?