Worst film? The original Spy Kids. I'd probably spend the entire movie riffing on it and laughing if I watched it now, but 12 or 13 year old me was incensed that they would try to push something this crappy on kids. [sub]I have had the phrase "Floop's Flooglies" burned into my brain ever since. Also the scene where they wake up a shark by peeing in a wetsuit -- never mind the fact that sharks don't sleep.[/sub]
Worst experience, presentation wise, would be anytime I go to an AMC theatre. I swear, they don't train their projectionists. Every film I've seen in one of those places since I was old enough to notice has been projected out of focus, with the sound track collapsed to mono -- and probably turned below reference level to boot. To add insult to injury, the individal theaters tend to smell like mildew. Crappy, crappy multiplexes. Cobb theaters, on the other hand, tend to be pretty good, and there's a local movie-house not too far from where I live to go every now and then, which is run by people who really care about movies, so it's got excellent presentation all the way round.