Trump calls Rex Tillerson 'dumb as a rock' after fired secretary of state says he kept having to say 'You can't do that'

WASHINGTON — Former Secretary of State Rex Tillerson on Thursday described former boss President Donald Trump as someone who is "pretty undisciplined," "doesn't like to read," and "doesn't like to get into the details of a lot of things."

The Texas native and former Exxon Mobil CEO didn't stop there.

"So often, the president would say, 'Here's what I want to do, and here's how I want to do it,' and I would have to say to him, 'Mr. President, I understand what you want to do, but you can't do it that way. It violates the law,'" he said at a rare public appearance in Houston.

That less-than-stellar job review, first reported by the Houston Chronicle, earned a quick rebuke on Friday from Trump.

Tillerson "didn't have the mental capacity needed," the president wrote on Twitter, saying Tillerson didn't measure up to current Secretary of State Mike Pompeo. "He was dumb as a rock and I couldn't get rid of him fast enough. He was lazy as hell."

The exchange is another bizarre chapter in the duo's relationship, one that started with great promise over the meeting of two famous business minds, then soured when Tillerson reportedly called Trump a "moron" and ended when the president fired Tillerson by tweet.

Tillerson, speaking at a fundraiser for the MD Anderson Cancer Center, said on Thursday that Trump had a much different style than his own.

"He acts on his instincts and, in some respects, that looks like impulsiveness," Tillerson told the moderator, CBS News' Bob Schieffer, according to The Washington Post. "But it's not his intent to act on impulse. I think he's trying to act on his instincts."

That approach was world's away from Tillerson's standard — the "disciplined, highly process-oriented Exxon Mobil corporation," he said.

"I didn't know how to conduct my affairs with him any other way than in a very straightforward fashion," he said, according to Politico. "And I think he grew tired of me being the guy every day that told him 'You can't do that, and let's talk about what we can do.'"

Tillerson also lamented the effectiveness of Trump's bombastic Twitter account.

"I will be honest with you," he said, according to the Chronicle. "It troubles me that the American people seem to want to know so little about issues, that they are satisfied with a 128 characters."

Trump response to Tillerson's critique was true to form.

The president didn't hold back last year when the reports emerged that his secretary of state called him a "moron." Even as he dismissed Tillerson's alleged insult as "fake news," he said at the time that if the diplomat "did that, I guess we'll have to compare IQ tests."

"I can tell you who is going to win," Trump said then.