Sorry Donald. People have been using this phrase way before you even dreamed of having a show. It was fist used to fire someone from a job. This usage has dropped of though because saying "You're Fired" might spark emotion. Instead now HR people use the words terminated or released to let someone know they were "Let Go".
My friends have been using it forever when someone screws up and they are pissed.
Example 1)
Donald: You're Fired
Me: I'm sooo over this show
Example 2)
Me: Oops I forgot to grab the camera honey.
Honey: You're Fired. I'm going to find me a new boyfriend.
An unsympathetic and merciless phrase which may be used by those with the power to hire and fire employees or contractors, when the services of those in their employ are no longer required.
Popularised by the entertainer Donald Trump on the TV show 'The Apprentice', before the majority of US voters decided to turn the phrase on him in November 2020.