If you are talking about best worst movie, my vote would be for "The Room". There are bad movies and then there are movies so incomprehensibly bad you swear an alien was the director of the film. The Room fits into the latter almost perfectly (minus the alien bit though that might be a plausible theory given the man who made it Tommy Wiseau has a mysterious origin and background that to this day not even his co-star and former friend Greg Sestero knows quite where Tommy is from nor where he got 6 million dollars to help finance production of The Room)
Take bad acting, sub-plots that go nowhere and only exist to pad out the 90 minutes, characters who have the memory of a goldfish who's motivations flip flop more than a bi-polar person's mood swings, some cringe inducing sex scenes that take forever to get through, and add a pinch of nonsensical and illogical non-sequiters that only the genius of Tommy Wiseau could've come up with and you've got The Room.
For those willing to take the plunge into the fascinatingly bizarre world of The Room, your best bet would be to watch either The Nostalgia Critic's review of it or watch CinemaSins tear it a new one.