I struggle with people who say “X was the worst film ever, I walked out after 20 minutes”. That’s a bit like saying “x is the worst song ever, I only listened to the first 14 seconds”.
In a moment of boredom we saw a film called “Extraordinary Measures” that was complete tosh, worst thing I’ve seen in the cinema.
Most seem to have been mentioned. Open Water I can let slide, as it’s based on a (supposed outcome of a) true story, it’s just an inherently uninteresting true story! Nicolas Cage is a great barometer for things to avoid.
The Village, and Speed 2 spring to mind as being really really rubbish!