LBJ had a history of indecent and vulgar behaviour. He liked to show off his "manhood" to people who challenged him.
The stories about LBJ's bad behavior that I've heard concern people much higher in the status hierarchy. I'm not an LBJ scholar, but I suspect much of this behavior was a twisted dominance game. He would ritually humiliate his targets, mostly (I suspect) people he suspected of thinking themselves intellectually or socially superior to LBJ: e.g., a Member of Congress or cabinet member or intellectual policy wonk who might look down on Johnson as a crude embarrassment. That's not an ego game he would have felt any need to play with the support staff. With them, I suspect he had an open, bantering relationship (not unlike Bill Clinton when Hillary wasn't around and when they weren't engaged in screaming matches).
I wish someone would write a good book on this subject. Not so many years ago, many people (especially liberals) would be surprised when Jesse Helms and Paul Wellstone annually topped the "most liked" or "nicest Senator" lists. Lefties always imagined Helms as a fire breathing monster. They were always surprised to find out that he was the Senator who knew the names of the elevator operators, the "walk and talk" ladies dishing out food in the Senate cafeteria, and the Capitol Police guy at the front door. Helms not only knew their names; he often asked about their wives and kids. He took care to know people he didn't need to know. Wellstone was the same way.