Occasionally we watch a movie that we regret spending our time on. That's a "bad" movie, often boring, and one we'll forget. Then we see something that makes you wonder how it ever got made. Along the way we start laughing because the poor acting, incomprehensible script, implausible premise, or a combination of those things are so over-the-top. These are the "so-bad-its-good" movies.
Jack Nugent of Now You See It (previously at Neatorama) explains how really great movies and so-bad-its-good movies have something in common. It's just that the great movies do it on purpose (and do it well), and the so-bad-its-good movies stumble upon it by accident. The result is that there are more clips from great movies in this video than from awful movies. And the lesson is that whether a movie is good or bad is less important than whether the movie is entertaining. -via Tastefully Offensive