I think the absolute worst movie I saw there was "The Dirt Bike Kid". Oh man, it wasn't even bad in a good way, like Showgirls is. It was just baaaaaad.
I also remember this movie "Iron Eagle", which was a total piece of crap, but during in the movie they play Twisted Sister's "We're not gonna take it", and a lot of the students had a shit fit and started, in RMA lingo, "fiending out", which I thought was hilarious 'cause I found Twisted Sister to be a totally crappy poser band. Anyway, they stopped the movie and yelled at us, and said they weren't going to start playing it until everyone calmed down, which they eventually did. So we actually did get to see the whole movie, which was a crying shame.