There's no thief like a bad movie.

The quip plays on the idea that a “bad movie” steals something valuable from the viewer—most obviously time, but also attention, money, and the opportunity cost of having watched something better. By calling it a “thief,” Ewing frames poor entertainment as an active wrong rather than a mere disappointment, sharpening the complaint into moral language. The line also implies a standard for art: when a film fails, it doesn’t simply fall short; it takes from its audience without giving the compensating pleasures (insight, beauty, excitement) that justify the investment. Its punchy absolutism makes it memorable and easily reusable as a general critique of wasted time.