In House of Cards, which is American TV series, the President AAA decided to offer Frank Underwood, who is a congressman, Vice Presidency. During their dialogue, Frank always addressed the President "Mr. President", but the President just called him his first name Frank, instead of Mr. Underwood.
Is it rude for Frank to address the President his first name AAA?
Lisewise, if my boss called me my first name, should I call him Mr. Johnson, or it is okay for me to call him Peter?
P.S. My boss name is not really Peter Johnson.
One would have to very, very familiar with the President of the United States to call him by his first name. Even then, for the sake of decorum, you would probably refer to him as "Mr President" when around others.
The use of a familiar/first name by one person who is in turn addressed as "Mr.... or Ms...." is a sign of the power dynamics.
Children call friends of their parents "Mr. X" or "Mrs. Y" in the US.
My children call my husband (their step-father) by his first name, but their friends call him "Mr. D" and I'm "Mrs. D."
Even now, as I approach 50, I call my parents' long-term friends (dating back to my childhood) "Mr. X" or "Mrs. Y" because that's how I think of them, unless they say "For heaven's sake, Barb, call me Joe!" or something similar. However, their new friends, whom I met as an adult, I call by their first names.
When I worked at a factory, the plant manager (a vice president in the company) was "Mr. Edwards" on the factory floor and "Paul" among the professional staff. He wouldn't have minded being called "Paul" on the floor but they just didn't. He called everyone by their first name, if he knew it.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
I remember an early West Wing episode (I think it was one of the tedious ones at the beginning of series 2) when Sam (one of the insiders) upbraided a fellow speech-writer for referring to the President as 'Bartlett' (even when the President himself wasn't there).