The "New York Post" says that ROBERT DE NIRO scolded JAY-Z at LEONARDO DICAPRIO'S birthday party last weekend.
Apparently, Jay had promised to record a song for De Niro's Tribeca Film Festival. But De Niro had been trying to get a hold of Jay to discuss the details, and Jay wouldn't call him back. So when Jay went over to his table to say hello, De Niro let him have it.
A source says, quote, "Bob 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."
Witnesses say Jay tried to joke his way out of the situation, and even BEYONCÉ tried to smooth things over . . . but De Niro wouldn't stand down.
The source says, quote, "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 source close to De Niro says it wasn't that bad . . . quote, "It was a low-key private conversation between two people that was apparently overheard. It was not a heated discussion."