"A movie, so bad, it's good". We all have used that expression before. But what does it mean?
Normally we seem to be able to clearly categorize films in good or bad. For example I love "The Empire Strikes Back" and consider it one of Hollywood's greatest achievements. M. Night Shyamalan's "After Earth" on the other hand, is a movie, that nearly bored me to death (which is an opinion, that the majority of its viewers would agree with).
But sometimes a movie fails so miserably at everything it set out to do...that it becomes enjoyable to watch. We do not enjoy "After Earth" because even though it fails at being entertaining and convincing, it does not go completely overboard with it and we still see it as a Sci-Fi flick (not a good one though).
Joel Schumachers "Batman & Robin" on the other hand absolutely failed at everything it tried to be - a continuation of the darker interpretation of the caped crusader. Every attempt at being serious or dark, seems so over the top, that the audience can't help but laugh and even though it does not consider the movie good by any chance, it is still somewhat entertained, because it knows exactly how a serious "Batman" should look like, and that this particular film looks rather like a comedy (without intending to be one).
Tommy Wiseaus' "The Room" is the epitome of exactly that. It's horrific over the top acting, its terrible dialogue, its inconsistent writing and plotholes are so far from being anything it tries to be, that it just comes of as a comedy, which is why "The Room" has become a cult classic for being THE movie, that is so bad, it becomes enjoyable.