Let me go off on a slight tangent before I answer because your question gave me a lot of ideas. I know you said movie but The Sopranos and The Seinfeld finales were really lame. I remember watching the film The Butterfly Effect and looking at the alternate ending on the DVD and saying the alternate ending was lame and am glad that they picked a good ending. The lamest movie ending that comes to mind is the Tim Burton Planet of the Apes. I am referring to when Mark Wahlburg ends up in Washington at the "Lincoln" Memorial. As the Ape planet happened in the future and the evil ape was disgraced and it was established that the planet they were on was definately not Earth, the ending made absolutely no sense and was a lame attempt to try to imitate (or should I say "ape") Pierre Boule's novel ending.