Picasa / WireImage 1 / 13
Picasa / WireImage 1 / 13

Fans of Jay-Z's lyrical stylings know how much he reveres Robert De Niro. He frequently name-drops the iconic actor, from the opening lines of "New York State of Mind" ("Yeah, I'm out that Brooklyn, now I'm down in TriBeCa, right next to De Niro") to "Party Life" ("Sippin' on my vino got me cooler than Pacino and De Niro put together, my real life is like 'Casino'").

But Hova managed to get on Bob's bad side by not practicing proper phone etiquette, says the New York Post, which claims the two ended up in a "tense beef" at Leonardo DiCaprio's celebrity-stuffed charitable birthday bash last weekend.

De Niro, in what sounds like a pitch-perfect recreation of his crankypants "Meet the Parents" character, reportedly took Jay-Z to task for not returning his calls over plans to record a song for the TriBeCa Film Festival.

"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," relays a big-eared spy. "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."

Jay-Z could have pulled any number of excuses out of his pocket ("I was busy with the election/Blue Ivy/running my empire/firing my assistant for never giving me messages") but instead, he laughed and sheepishly explained he's "terrible on the phone," according to a source.

"De Niro kept telling him that he thinks he's the man," recalls the snitch, "but that he was disrespectful.'"

Perhaps sensing her husband was in trouble, Beyoncé came over, but it seems she was unable to smooth things over.

"It was the talk of the party," marvels the source. "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."

As his turn as a baseball bat-wielding Al Capone in "The Untouchables" proved (and "Raging Bull," and "Cape Fear" and, well, you get the idea). Still, another insider insists the pair's confab over call-return conduct has been overblown.

"It was a low-key private conversation between two people that was apparently overheard," a De Niro confidant tells the paper. "It was not a heated discussion."