Nearly two years into Donald Trump’s presidency, I thought I had lost my capacity for being shocked at the behavior of the leader of the free world. But on Friday afternoon, the president proved that he could still surprise me when he tweeted a string of insults at Rex Tillerson, his former secretary of state, that were crude and childish even by Trump’s standards.

“Mike Pompeo is doing a great job, I am very proud of him. His predecessor, Rex Tillerson, didn’t have the mental capacity needed,” Trump wrote. “He was dumb as a rock and I couldn’t get rid of him fast enough. He was lazy as hell. Now it is a whole new ballgame, great spirit at State!”

Tillerson did give Trump ample reason to be mad. On Friday morning, he gave a no-holds-barred interview with CBS’s Bob Schieffer on his time in office, painting a not-very-impressive picture of the president. Trump, according to Tillerson, “is pretty undisciplined, [and] doesn’t like to read”; the president would, in Tillerson’s telling, frequently propose new policy ideas that were clearly illegal.

Obviously, Trump couldn’t let that kind of comment from a former top aide just slide without a response. But the way he chose to respond — hoo boy. Look at it again:

Mike Pompeo is doing a great job, I am very proud of him. His predecessor, Rex Tillerson, didn’t have the mental capacity needed. He was dumb as a rock and I couldn’t get rid of him fast enough. He was lazy as hell. Now it is a whole new ballgame, great spirit at State! — Donald J. Trump (@realDonaldTrump) December 7, 2018

The man who wrote these words is in charge of the world’s most powerful country, with a world-class military and a nuclear arsenal large enough to incinerate the planet. And yet here he is, lobbing insults like “dumb as a rock” and “lazy as hell” at someone he once picked to be America’s top diplomat.

The pettiness and impulsivity on display here would be pretty funny if it weren’t so scary.