He is famed for playing characters with explosive tempers, but it seems that when Robert De Niro loses his temper in real life, it can be just as bad.
According to the New York Post, the 69-year-old Godfather actor gave the music mogul a stern dressing-down because he had failed to return not just one, but six of his calls.
Jay-Z had apparently agreed to record a track for the Tribeca Film Festival, which De Niro was involved with, but failed to follow through.
Witnesses at the star-studded party claim that things turned sour when Jay Z approached the actor to say hello.
"Bob was sitting at a table, and when Jay-Z went over to say hello, De Niro told Jay that he never called him back," a source told the New York Post.
"[De Niro] wasn't in any mood to make polite conversation," the source says. "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."
Another source told the newspaper that despite Jay Z's wife Beyoncé's attempts to diffuse the situation, the Raging Bull star refused to back down and was in no mood to be friendly.
"De Niro kept telling him that he thinks he's the man, but that he was disrespectful," the insider said.
"Beyoncé came over, but that didn't calm Bob down."
They added: "It was the talk of the party. Everyone was saying there's only one star in New York bigger and badder than Jay-Z, and that's Robert De Niro.
"He can be quite scary when he's angry."
A host of A-list stars including Cameron Diaz, Mark Ruffalo, Emma Watson, Chris Rock, Jamie Foxx and Martin Scorsese attended the bash to celebrate Leonardo's 38th birthday.
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