Nominations thus far:
* SredniVashtar?If we are suggesting recent movies (as above) , I would posit that either of the following are much more likely.
* Cold MountainQuite a few qualities of sadness on your list, as well. Some tear-jerkers, some O Henry-esque surprises.
When I saw AiTheMovie on this list, my first thought was that it should be on a page called TheBaddestEnding, with bad meaning not good, and baddest chosen because it rhymed with saddest. But now that page has been transmogrified into one where bad means good, so I think AiTheMovie is an example of TheWorstEnding a movie can have.
I thought that AI is probably the best current example of why films should not be shown to Focus Groups before the final editing phase. It seemes pretty clear (to me at least) that the intended ending was about 10 minutes before the actual ending (I'm trying to avoid spoiliers here, but if you have seen the film I'm sure you know which point I mean here). -- IanPhillips