Robert DeNiro testified at his civil trial against his former assistant … and he got into some heated exchanges with opposing counsel, uttering at one point, “This is all nonsense!”

The Oscar-winning actor took the stand in an NYC courtroom for most of Monday afternoon — and he appeared grumpy as he tried to keep his anger in check, which, at times, leaked out.

During his testimony, DeNiro said he had previously made Graham Chase Robinson his emergency contact and depended on her to get greeting cards for his kids.

When Robinson’s attorney asked if she was a diligent worker, DeNiro sneeringly replied, “Not after everything I’m going through now.”

At another point under cross-examination, DeNiro became hot under the collar, while coming to the defense of his girlfriend, Tiffany Chen, who repeatedly clashed with Robinson and accused her of being in love with the superstar. In a pointed manner, DeNiro testified that he and Chen “make decisions together.”

Then Robinson’s lawyer implied that De Niro annoyed his client one morning in 2017 when he needed to be brought to the hospital.

DeNiro seemed pissed, testifying, “That was one time when I cracked my back falling down the stairs!” He added that he put off calling Robinson after the accident, waiting several hours to contact her at a more reasonable time.

The biggest blowup came when DeNiro defended what he described as his good treatment of Robinson after purchasing a five-bedroom Manhattan townhouse.

DeNiro testified, “It is not like I’m asking for her to go out there and scrape floors and mop the floor. So this is all nonsense!”

The courtroom drama stems from a $6 million lawsuit Canal Productions filed against Robinson after she quit her $ 300,000-a-year job at the company.

From 2008 to 2019, Robinson worked as DeNiro’s personal assistant and was eventually promoted to Vice President for Production and Finance at Canal. In the suit, Canal claimed Robinson watched Netflix all day while on the clock, among other complaints.