Bad movies are made all the time in the film industry (shocking, I know). While no one sets out to make a bad film, sometimes the film becomes one for a variety of reasons. Sometimes you are stuck with a poor script or poor actors; other times you face production troubles, such as poor effects work and a shortened shooting schedule, that leads to the films messy production effecting the film.
There are many reasons why a film can come out bad, but that's not what I'm here to talk about. I'm more fascinated by what makes a film "so bad, that it's good". This is a phrase often used to describe films that are clearly terrible, but their unique form of terribleness adds a uniquely enjoyable and interesting quality to the obviously bad film.
We see this describing certain bad films all the time, such as "The Room", "Birdemic: Shock and Terror", "Sharknado", and "Dungeons & Dragons". What is it about these films that give them funny and enjoyable, while other bad films just end up angering you or become boring? Like most ideas in film, there are many factors that lead to these films being "enjoyably bad".
One aspect of an "enjoyably bad" film is the hilarious levels of incompetence when it comes to the technical aspect of film making. Things such as lighting, framing, sound editing, acting, and special effects are so bad that you can't help but laugh and wonder how anyone working on the film thought that this was good enough to release. These are the qualities that made "Birdemic: Shock and Terror" so entertaining.
The film has hilariously stiff acting to the point were these people don't even sound and behave like real human beings. The camera work, lighting, and sound editing is lower in quality than those of the budgetless films I made in College (which is hilariously sad). The hilariously awful looking CG on the birds and the way they dive bomb and explode on impact was the most iconic thing about the film.
This brings me to the next aspect of a "enjoyably bad" movies, ideas and concepts that are so insane that they make the film memorable. These ideas are so crazy that they are enjoyable to watch just so you can say, "that's a thing that I saw in an actual movie". The Syfy Channel has pretty much cornered the market on these ideas, one of the most popular being "Sharknado".
The entire point of the film is to enjoy the sheer ludicrousness of the concept of tornadoes full of man eating sharks entering a city and attacking people in hilarious ways. You also get to enjoy the spectical of watching our heroes kill the sharks in over-the-top gory ways (like chainsawing a shark in half or blowing up a tornado). It falls into that "you have to see it to believe it" level of audacity that makes you seek it out.
The last aspect I will discuss is a misguided attempt at legitimacy. Many films try to aim for greatness, but sometimes they come up short in their quest to meet their lofty goals. This usually comes as a result of attempting to replicate what worked in great films, but not being able to comprehend why they worked in those films. This is what happened with "The Room".
Director/Actor Tommy Wiseau seems to have tried to make a serious character drama with all the aspects that make up most dramas in Hollywood. Dramatic music, passionate protagonist, and an attempt at "emotional" acting. However, the bizarre pacing and strange acting from Wiseau make the film more funny than dramatic, but it also gives the film a sort of endearing quality, like your kid's finger-paintings that you put on the fridge. They won't win any art awards, but you celebrate what they attempted.
Wiseau also made the film memorable due to his wierd performance. He acts like an alien who has never met an actual human before and is trying to mimic their behavior. Strange performances can also make bad films worth seeing. If you want proof of this just watch Jeremy Irons' hilariously hammy and over-the-top evil performance in "Dungeons & Dragons" for that.
These are only a few of the reasons why some bad films become enjoyable classics. There is no distinct formula to making a "so bad, it's good" movie, which is what makes them so mysterious and unique. "Enjoyably bad" is not a quality that can be easily replicated, it is instead something that happens naturally when all the right circumstances are in play.