"Swearing contextually has a lot to do with power," said Tim Jay, a professor of psychology at the Massachusetts College of Liberal Arts who specializes in studying swearing.
It establishes hierarchy, since the boss can cuss at you but you aren't likely to cuss at the boss.
"It's also a way of communicating expectations and the level of involvement and urgency of those expectations," Jay said. Think hockey coaches trying to motivate players in the heat of the playoffs.
In addition, an occasional expletive can become part of the mystique of the leader.
"It's part of the leadership status but also part of the persona," Jay said. "The person didn't come into the position without a history. You don't become a CEO and then start swearing. That was part of the persona that got you the position. It may have made you seem assertive or direct."
Also, the professor noted, curse words and trash talk can keep competitors at bay and enforce a leader's street cred. (Possible example: The Ackman-Icahn Face-off)