The Dark Backward (1991)
[3]
In a dystopian world full of garbage and stained walls, an unfunny comedian (Judd Nelson) starts growing a third arm out of his back. His super-annoying friend (Bill Paxton at his worst) sees the aberration as his ticket out of hell and exploits it for all its worth. A smarmy talent agent (Wayne Newton) decides to rep them, and an even bigger agent (Rob Lowe) decides to bring them to Hollywood. But then the arm disappears and the poor unfunny comedian learns who his true friends are. Spoiler alert: he hasn’t any.