Reports say that Robert De Niro dissed Jay-Z last week at Leonardo DiCaprio's birthday party in NYC. According to The New York Post, De Niro is upset at Jay-Z because he wanted Jay to to record a song for the Tribeca Film Festival -- which was co-founded by De Niro in 2002, but he never returned his calls. A source said, "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. 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." Another source said, "De Niro kept telling him that he thinks he's the man, but that he was disrespectful. Beyonce came over, but that didn't calm Bob down." Jay reportedly tried to joke it off, but De Niro was very upset.