"Worst" is such an arbitrary concept that I don't know what to say. For example, since Allaby brought up Manos: The Hands of Fate, something I've said before is that I have more respect for that film – made by an inexperienced filmmaker with an inexperienced crew and a shoestring budget, and as a result of a bet – than I have for a big budget, nonsensical mess like Transformers, which is made by an "experienced" filmmaker.
Then you have stuff that is ineptly made, but often purposefully so. For example, Thankskilling – a film about a killer turkey – is by most metrics, a bad film full of bad acting, bad script, and bad production values. But at the same time, it has one of the most stupidly hilarious sequences I've seen on a film that had me in tears from laughing, so how can I fault it if that's what they were aiming for?
So in the end, I guess there's a mixture of the filmmakers original intent and resources, with my expectations of a film. That all factors into whether or not I consider it a "bad" film. Stuff like Speed 2 or A Good Day to Die Hard are good examples.
Then you have stuff that is ineptly made, but often purposefully so. For example, Thankskilling – a film about a killer turkey – is by most metrics, a bad film full of bad acting, bad script, and bad production values. But at the same time, it has one of the most stupidly hilarious sequences I've seen on a film that had me in tears from laughing, so how can I fault it if that's what they were aiming for?
So in the end, I guess there's a mixture of the filmmakers original intent and resources, with my expectations of a film. That all factors into whether or not I consider it a "bad" film. Stuff like Speed 2 or A Good Day to Die Hard are good examples.