By Nick Romano
September 15, 2018 at 10:55 AM EDT

Former Secretary of State John Kerry didn’t want to “riff” too much on President Donald Trump when he sat down with Bill Maher on HBO’s Real Time Friday night. But coupled with what the commander in chief tweeted about him this week and the audience member egging him on, he indulged himself.

“He’s got the maturity of an 8-year-old boy with the insecurity of a teenage girl. That’s just who he is,” Kerry said.

It all started when Maher asked Kerry why Trump seemed to be mad at him, to which he replied, “I don’t know. I think I told the truth.”

Trump tweeted on Thursday, “John Kerry had illegal meetings with the very hostile Iranian Regime, which can only serve to undercut our great work to the detriment of the American people. He told them to wait out the Trump Administration! Was he registered under the Foreign Agents Registration Act? BAD!”

Kerry was very upfront about that meeting. “Everybody does,” he said. “Henry Kissinger [another former Secretary of State] for 40 years has been traveling to Russia, traveling to China, talks with the leaders. There’s absolutely nothing usual about it. The conversation I think he really ought to be worrying about is Paul Manafort with [special counsel Robert] Mueller.”

Manafort, Trump’s former campaign chairman, pleaded guilty to criminal charges pertaining to his political consulting work in Ukraine. This was part of a plea deal with Mueller’s investigation into interference with the 2016 presidential election.

“It really is giant, and soon you will be hearing him say, ‘That’s the worst deal that’s ever been made,'” Kerry remarked. “When you stop and think about it, it’s gone from the ‘art of the deal’ to the ‘art of the squeal.’ I, honestly, have never seen anything quite like it: the anonymous [New York Times] op-ed, the [Bob] Woodward book, the chronology of everything that’s been happening. And it’s tough.”

“Unfortunately,” he added, “we have a president, literally, for whom ‘the truth, the whole truth, and nothing but the truth’ are three different things, and you don’t even know what they are.”