Who was it that said Donald Trump would start acting more presidential after the inauguration? Oh, yeah, pretty much everyone who voted for the toddler-man. Boy, were they wrong. Monday at the White House provided a perfect example of how Trump’s immature and undermining behavior extends beyond the Twittersphere.

President Trump should thank his lucky stars every day that South Carolina Governor Nikki Haley accepted his offer of being the U.S. ambassador to the U.N. She’s already been an amazing asset for the U.S. at the U.N. But what does he do instead? Puts his foot in his mouth by insinuating Haley could be “easily replaced” if the other ambassadors didn’t like her.

Here’s how the moment went down:

Trump was kicking off Monday’s lunch with ambassadors of countries on the U.N. Security Council when he asked the room if they liked Haley, the U.S. ambassador to the U.N. Trump said that if they didn’t, “she could easily be replaced.” The comment sparked some awkwardness, but seemed to be taken in jest. Haley and others gathered around the lengthy table laughed. Trump quickly assured Haley her job was safe. “I promise, we don’t do that,” Trump said, and praised Haley for doing a “fantastic job.”

Yes, it was a joke. But here’s the thing: It was a joke about someone being removed from her job in a room full of people Trump doesn’t know well. There’s something about knowing your audience and acting accordingly, and joking that your own U.N. ambassador could be removed if her colleagues in the U.N. Security Council don’t like her undermines Haley’s position and her authority to speak for the president.

Trump, in likely an attempt to remind everyone that he’s the bully in charge, not his ambassador who garners praise on a regular basis, only showed his immaturity and capricious nature that he would even hint at something like that.

Grow up, Mr. President. You’re dealing with adults now. Act like you can handle the responsibility of effective international diplomacy and stop embarrassing those representing your administration, especially those who are clearly your betters.