Lots of parents do, talking to their young children.
I’ve never actually met anyone who does this, but it brought to mind a story about actor William Boyd, who famously played “Hopalong Cassidy” in movies and on TV. He supposedly would refer to himself as “Hoppy.” It was like he was speaking for his character, not himself. Like Hoppy was a real person.
“How would you like to play a circus?”
“Sure. Hoppy loves the circus.”
or
“Would you make an appearance at a supermarket opening?”
“No, Hoppy doesn’t do supermarket openings.”
People thought it was weird. Boyd was a really smart man, though. The studio that made his old movies thought they were worthless. He bought the rights, sold them to television and made a fortune. He had a whole new career thanks to that.
Hoppy was a pretty good businessman.
I vaguely remember seeing him at the circus when I was very young, but I vividly remember seeing him on TV.
I do it in my head.
Oh, crap. Now y’all know I’m hearing voices.
I’m not crazy, been examined. 
We prefer first person plural.
WE insist on the majestic plural.
We too do that.
I would like a cite for this, unless it is just another dig at trump. My cite showed otherwise.
RPG = appropriate. But show biz folk? Oh man, that explains a lot.
To me, it’s SO weird.
And also funny, as in “Jimmy really likes Elaine.”
Yes, I did. I stayed in a boarding house in Beaverton, OR, one summer and there was another boarder there named Dave. He was…not quite right. In fact, both of the other boarders had some mental issues and I believe that the owner of the house was in a program where people were referred to her from a state agency. (Of course, I fit right in.)
Dave was ordinarily very cheerful and ALWAYS referred to himself as “Dave.” However, he had some anger management issues and could change in a flash. It turned out that he also preferred us to refer to him as “Dave” whenever we were talking directly to him.
“Yes, sir, Dave’s going down to the bowling alley after work!”
“Is Dave a good bowler? What is Dave’s high score?”
“Dave has bowled a 240.”
Obligatory Mitchell & Webb clip:
Baseball player Rickey Henderson was also notorious for speaking in the third person.
“Ricky going to take off!”
I’ve never known anyone who referred to themselves in the third person - even surgeons, who are more prone to narcissism than other physicians.
There are plenty of examples.
In the Robert Philip Hanssen biopic Breach, he’s shown doing this from the backseat immediately after his arrest.
More blind Youtube links, which prove absolutely nothing. My cite stands, your YT do not.
Sure trump refers to himself in the third person, and he seems to be a narcissist.
But he also has children- does this mean anyone who has kids is a narcissist? He has a bachelor’s degree in economics- that clearly means that everyone with such a degree is a narcissist, right? 
I do not give a good goddamn that trump often refers to himself in the 3rd person- that is not in any wayshapeorform an argument that everyone who does that is a narcissist. Get over it.
My cite stands.
and here is another
Surprisingly, there’s little research or anecdotal evidence that the habit is more common among narcissists, according to Elinor Greenberg, the author of the book, “Borderline, Narcissistic, and Schizoid Personality Disorder: The Pursuit of Love, Admiration, and Safety.” “Half of my practice is people in treatment for narcissistic personality disorder. None of them refer to themselves in the third person,” she said. “It is really not common at all.”
That article did point out something that hadn’t occurred to me. Many of us probably have used the third person when talking to small children, such as “Daddy has to work late tonight.”
Re: Trump, the author points out:
In the case of Trump using third person, Chris Stevens, a psychologist and the host of the podcast “Psychology to Live By,”believes it’s “grandiosity, pure and simple,” not some ironic joke or a self-care strategy.
Not all people who refer to themselves in the third person are narcissists. But narcissists who do so as a function of their narcissism - well, there’s an undeniable connection there.
Sound like anyone you know?
*“Talking to a narcissist is like talking to a brick wall”. Of course, that doesn’t mean that a person who presents as a brick wall is necessarily a narcissist. 