"Dinner Theatre" is considered the last refuge for failed actors... at least in general folklore and common parlance.
Dinner theater (sometimes called dinner and a show) is a form of entertainment that combines a restaurant meal with a staged play or musical. "Dinner and a show" can also refer to a restaurant meal in combination with live concert music, where patrons listen to a performance during a break in the meal. In the case of a theatrical performance, sometimes the play is incidental entertainment, secondary to the meal, in the style of a night club, or the play may be the main feature of the evening, with dinner less important or, in some cases, optional.
Basically, the threat is that if the performers do not get their act together they will have no choice but to go back to performing at the "lowest" form of their craft they can get.