Does the President demean his aides with “You’re fired!” ?

Not that President; t’other one.

The time is August, 1963.  JFK was annoyed and disgusted with his aide.

After the meeting, Forrestal approached Kennedy  and offered to resign.
“You’re not worth firing,” the President said.  “You owe me something, so stick around.”

-- Richard Reeves, President Kennedy:  Profile of Power (1993), p. 568