This is a bit weird, since I do have a special fondness for so-bad-they're-funny B movies. On the other hand, if a movie - however well produced - doesn't inspire, engage, or entertain me, or if it upsets me, I will leave. I've left over simply just losing interest in a movie. I simply don't sit through a movie if I don't deem it worth my time. So the two worst movies I sat through are Election Day and Tim Burton's Planet of the Apes. In the former, I hated every single character so much, I might have been happier if suddenly a nuke dropped on them or perhaps even on me. The other was OK-ish if I didn't consider it part of Planet of the Apes canon... until the ending wrecked even that. The only reason I tortured myself in sitting through them is because we paid for theater tickets.
At least the fun part was that the husband and I hated them together.