5 other times Mattis dropped terrifying threats on people Mattis don't mince words, and if he has a problem with you, he will f***ing tell you.

Secretary of Defense Jim Mattis didn’t favorably receive former Press Secretary Sean Spicer’s repeated requests to get the retired Marine Corps general to appear on numerous talk shows, according to an excerpt from Bob Woodward’s upcoming book, “Fear: Trump in the White House."

According to one passage in the book, an exasperated Mattis, having answered “no” a number of times already, lashed out at Spicer, who is an officer in the Navy Reserve.

“Sean, I’ve killed people for a living," the secretary of defense said. "If you call me again, I’m going to f--king send you to Afghanistan. Are we clear?”

To date, Mattis has appeared only once on a network television show, when he added to his long list of Mattisisms after “Face of the Nation" host John Dickerson asked what tumultuous world affairs keep the retired general awake at night.

“Nothing. I keep other people awake at night,” he quickly countered.

Since then, however, Mattis’ distaste for the limelight has been clear. At a recent Pentagon briefing, he told reporters that standing in front of cameras and addressing large audiences is something he dreads, according to Business Insider.

The exchange with Spicer is one of many noteworthy examples in “Fear” that illustrate the divide between the White House and the Pentagon.

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In one section, Woodward recounts how the president’s disconnect from matters of national security prompted Trump to question why the United States was even allocating military resources to the Korean Peninsula at all.

“We’re doing this in order to prevent World War III,” Mattis answered.

“Mattis was particularly exasperated and alarmed," following the Jan. 19 National Security Council meeting, Woodward writes, "telling close associates that the president acted like — and had the understanding of — ‘a fifth- or sixth-grader.’”

That statement was refuted by Mattis on Tuesday, when the secretary of defense called Woodward’s book a work of “fiction” and “a product of someone’s rich imagination.

“While I generally enjoy reading fiction, this is a uniquely Washington brand of literature, and his anonymous sources do not lend credibility," Mattis said in a statement.

Woodward based “Fear” on hundreds of hours of interviews with Trump administration staffers with firsthand experience conducted on “deep background," according to the Washington Post.

In addition to Mattis, chief of staff and retired Marine Corps Gen. John Kelly features prominently in Woodward’s White House exposé, and is quoted as saying the president is “unhinged,” according to the Post.

“He’s an idiot,” Kelly is reported as saying about the president. "It’s pointless to try to convince him of anything. He’s gone off the rails. We’re in Crazytown. I don’t even know why any of us are here. This is the worst job I’ve ever had.”

These statements, like those reportedly made by Mattis, were also refuted.

“The idea I ever called the president an idiot is not true,” said Kelly, who called Woodward’s work "another pathetic attempt to smear people close to President Trump and distract from the administration’s many successes.”

The chasm of communication and decision-making that has existed between the White House and Pentagon on matters of national security has led many to speculate that an exhausted Mattis may step down before Trump’s first term even draws to a close.

Those close to the secretary of defense, however, have insisted that he will remain for the duration of the term if asked.