While De Niro's outburst received accolades from the anti-Trump #Resistance, it was the president's fans' turn to gloat after the twitter response. "I watched him last night and truly believe he may be 'punch-drunk, '" the leader of the free world tweeted.
Trump, sounding a bit furious, posted a series of tweets against Robert De Niro.
With both men septuagenarians a meeting in the ring is unlikely, but you can expect this feud to run and run.
De Niro has attacked Trump on previous occasions, describing him in 2016 as "blatantly stupid", "totally nuts" and an "idiot". In January, De Niro referred to him as the "baby-in-chief" at the National Board of Review Awards.
The actor, a noted liberal, has been increasingly critical of Mr Trump, a Republican, at smaller show business events in the past year, but none of them had the profile of the Tony Awards.
Lucas Jackson Reuters Robert De Niro made the comment as he welcomed Bruce Springsteen to the stage
At Sunday night's Tony Awards, De Niro launched an expletive at Trump.
And his tweet Tuesday was not the first time Trump had called someone a "low IQ individual".
De Niro was introducing Bruce Springsteen, who is starring in a Broadway production of his own, which has sold out tickets for months.
De Niro went off script in the Tony Awards telecast, and the offensive language was deleted from the broadcast, the CBS reported.
It'd be amusing if it wasn't such a transparent glimpse into the mind of Trump, a man whose mood is buoyed entirely by famous people saying nice things about him. And I apologize to [Canadian Prime Minister] Justin Trudeau and the other people at the G7.