Former Secretary of State John Kerry was on Real Time With Bill Maher on Friday and didn’t waste the opportunity to mock President Donald Trump’s frequent use of social media and his thin skin. The former senator from Massachusetts, who is promoting his new memoir, said Trump is the first president “who spends more time reading his Twitter ‘likes’ than his briefing books or the Constitution of the United States.” Kerry made the comments as he pushed back from an attack earlier in the week from Trump, who questioned on Twitter why the former secretary of state had met with Iranian officials.

Kerry went on to say that he has “never seen anything quite like” the parade of critical accounts of the presidency, including the New York Times op-ed and Bob Woodward’s book. “Unfortunately, we have a president, literally, for whom the truth, the whole truth and nothing but the truth is three different things, and you don’t even know what they are,” said Kerry.

“I don’t want to get into a real riff on this but I’ve got to tell you,” the 2004 Democratic nominee for president said. An audience member at that point egged him on: “Do it!” Kerry smiled and continued: “He really is the rare combination of an 8-year-old boy—he’s got the maturity of an 8-year-old boy with the insecurity of a teenage girl.”

On Thursday night, Trump blasted Kerry on Twitter, saying the former senator “had illegal meetings with the very hostile Iranian Regime.” Kerry responded the next day, writing on Twitter the president “should be more worried about Paul Manafort meeting with Robert Mueller than me meeting with Iran’s FM.” And then he plugged his new book. On Maher’s show, Kerry insisted there was “absolutely nothing unusual” about his meetings.

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! — Donald J. Trump (@realDonaldTrump) September 14, 2018

Mr. President, you should be more worried about Paul Manafort meeting with Robert Mueller than me meeting with Iran's FM. But if you want to learn something about the nuclear agreement that made the world safer, buy my new book, Every Day Is Extra: https://t.co/DKjc33Kvvu https://t.co/cesltkt0zW — John Kerry (@JohnKerry) September 14, 2018