(UK definition)
A person who can't play another role than himself.
If every actors were like Jim Parsons,
the Oscars would be called the Big Brother Awards.
Abbrev. :
JP, e.g., to be a JP, to act like a JP.
Antonym : Brad Pitt, a person who can run, who can field, who can throw, who can hit and who can hit with power.
Director : "It's your turn, let me see what you got"
Actor : "hum, hum...
to BE or not to BE !!!"
Director : "Well, you're a big fat JP ! I guess your role will be
the doorknob..."
Actor : "
That's not fair, I'm not a Jim Parsons!"