Mary Trump said her uncle Donald Trump’s inability to laugh at himself is a “dangerous” trait that can be traced back to at least a humiliating incident in his childhood, which she called the former president’s “origin story.”

On TikTok this week, the presumptive GOP presidential nominee’s niece recalled the time her father Fred dumped a bowl of mashed potatoes onto his younger brother Donald’s head to stop him from tormenting their younger brother Robert.

Donald stopped acting out and Robert stopped crying, she said.

But then everyone started laughing at Donald and he “probably felt humiliated for the first time in his life,” she continued.

The incident was frequently brought up at family gatherings and “every single time, even six decades after the event itself occurred, Donald reacted exactly the same way,” said Mary Trump, who is one of her relative’s biggest critics.

“While everybody was laughing about it, he crossed his arms. And he pouted and he sulked until somebody changed the subject,” she said.

In another video on TikTok, Mary Trump explained the significance of the moment that has entered “family lore.”

“I think it says something about Donald that even as a little kid, he was incapable of having a sense of humor about himself, which is really not great,” she said.

“Kids need to have that kind of resilience that he never had,” she added. “But worse, at seven decades later, he still does not have the ability to laugh at himself, which I think is a dangerous thing.”