How T-Mobile USA CEO John Legere is changing the CEO game

How's this for authenticity: T-Mobile USA CEO John Legere has no qualms about dropping an 'F'-bomb right in the middle of a press conference.He's been taunting his rivals on Twitter long before that became the new standard in diplomacy.

More important than all of that, Legere is growing the rolls at the third-largest U.S. wireless carrier at a dizzying clip. T-Mobile added 2.3 million subscribers in the first nine months of last year. AT&T and Verizon might be bigger, but T-Mobile is bold, scrappy, and changing the rules of the game.

That's why Fortt Knox sat down with Legere to talk about how he decided to be a different kind of CEO, and why.

"The trick for me is, I really believe that I act, behave, and speak the same way my customers do. I say what they think on behalf of them," Legere told Fortt Knox. "If you look, most of my colorful nature and antics is to drive change that benefits customers."

The latest change T-Mobile is driving: Simpler phone bills. At the Consumer Electronics Show, Legere held a press conference to promote T-Mobile's vision, and call out competitors who he argued are overcharging.

As always, Fortt Knox tried to tease out a few lessons the rest of us can apply to our careers:

Legere grew up in Fitchburg, Mass., one of five brothers and sisters. The family didn't have a lot of money. He threw himself into sports, and had zero dreams of running a phone company.

"I wanted to be a foot doctor. I have no idea why. I was a runner. I thought that would be a great idea," he said. "I know when I was young, the last thing I wanted to be was an executive."

After a series of corporate jobs, Legere ended up in charge at T-Mobile, a company that needed attention and a turnaround. "Ultimately in this job, I was able to be who I am, and it worked."

Another guy who achieved success by being himself and ditching convention? The newly inaugurated President of the United States, Donald Trump. (The president also knows his way around Twitter.) Lessons from Trump's electoral victory don't escape Legere.

"He's got game," Legere told Fortt Knox. "I tell you... he is ignoring norms that I ignored as a CEO," he added.

"When I first came in, I remember our legal departments were like 'You don't do …' and he just keeps moving past 'don't do.' The reach and the breadth of what he's able to do – I don't know where it goes, but he's got game," Legere said.

Legere is on social media—a lot. Which might seem strange, until you consider the fact that he's the CEO of a company that's selling mobile Internet service, and social media and video are the main drivers of demand for his product.

"Slow Cooker Sunday" is literally a live online show Legere does on Facebook on Sundays, where he makes something in a slow cooker.

Don't laugh: the January 15 episode got more than half a million views.

"It may sound crazy, and this is why I know so much of what I do as a CEO the other guys aren't going to do – I use social media," he said. "I have hashtag #ShoppingSaturday. I use Instagram and I use Facebook when I go shopping on Saturday to buy the ingredients for Slow Cooker Sunday."

Legere is unconventional. Yet there's a strategy behind all of it.

Fortt Knox is a weekly podcast from CNBC anchor Jon Fortt. Previous broadcasts of the program can be found here.