Mr. De Niro then flexed both of his arms before quipping, "Now I'll get to my introduction".
The Tonys were being broadcast live on CBS in the United States, with censors managing to bleep the actor's profane message. "Who's gonna argue with him?" he said.
The audience responded by giving the actor a standing ovation.
De Niro is in Toronto for a groundbreaking ceremony for the Nobu restaurant and hotel, a project that the Oscar-winning actor is invested in.
She noted that De Niro's remarks came on the heels of comedian Samantha Bee calling first daughter Ivanka Trump a "feckless c--."
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Playwright Tony Kushner also shared De Niro's dismay of Trump saying it was a "the Hitler mistake" that put a "borderline psychotic narcissist in the White House".
According to US Today, Tony Award victor John Tiffany, who won for his role in the hit Broadway show Harry Potter and the Cursed Child, was making his way into the media room just as the Meet The Focker's actor went rogue.
"After De Niro, CBS told us to do something drastic, so here we are", Groban joked. "Boy, do we need that now!"
"He talks how he'd like to punch people in the face?"
Stewart acknowledged that everyone is "entitled to their opinion" but added that "it's offensive to many of us to hear that kind of language on live TV".
There may not be any angels in America, but according to De Niro there's at least one devil.