noun
actor who is brilliant on stage but hopeless at everything else
Describes a person whose entire life revolves around acting, often to the point of being incompetent or clueless in daily matters. Can be used affectionately or critically.
彼は役者馬鹿で、芝居以外のことは何もできない。
He's a stage-obsessed actor who can't do anything besides acting.
noun
dedicated actor; actor who lives and breathes acting
Colloquial term for someone who is utterly devoted to acting, often implying a single-minded passion. The nuance can be positive (admirable dedication) or slightly negative (obsessive).
あの役者バカは、休みの日もずっと稽古している。
That acting nut spends even his days off rehearsing.
Compound of 役者 (actor) and 馬鹿 (fool, idiot). The term likely arose from the idea that an actor so devoted to their craft becomes foolish or useless in other areas of life.