It was a celebrity war of words at Leonardo DiCaprio's birthday party the other night. Robert DeNiro was apparently upset with Jay-Z for neglecting to call him back, and called the music mogul out on it, the NYPost reveals.

Reports say that DeNiro gave Jay-Z a piece of his mind while celebrating Leonardo DiCaprios' birthday. This was all because Hov had never returned DeNiro's call. Apparently Hova's baby mama, Beyonce, tried to quell the beef, but DeNiro wouldn't back down.

This all happened when Jigga went over to DeNiro's table to say a friendly hello. DeNiro brought up the fact that Jay-Z never called him back, and as well, Jay-Z, who is a TriBeCa resident along with DeNiro, was supposed to record a song for the TriBeCa Film Festival, which he failed to do.

A source says, “[Robert] wasn’t in any mood to make polite conversation. He told Jay that if somebody calls you six times, you call them back. It doesn’t matter who you are, that is just rude.” 

Jay then reportedly tried to joke his way out of the matter, saying he wasn't good on the phone, but DeNiro was having none of it, and said the rapper was disrespectful.