Until last fall, I used to see a lot of movies in the theater, so this is a tough choice for me. I've seen many bad ones. However..
My choice for worst movies.. is a tie between Leaving Las Vegas, from 1995, which was basically a movie about Nicolas Cage having a last fling in Las Vegas, with the intent of killing himself. Some of the critics loved it. I hated it, as did my friends who saw it, and my mom, and her friends who saw it.
My other "Worst movie" was one I posted about on here.. I believe about a year or so ago. All About Steve. In spite of a good cast that included Sandra Bullock, the movie just sucked! Oh.. apparently whoever rates movies for TV/Cable agreed with me, because it got only one star, when it was shown on the premium channels.
So, those are my top two worst movies ever. Leaving Las Vegas, and All About Steve. I'm sure I can think of others, but those are the ones that stand out off the top of my head.
Mitch