Most of this list could be horror movies.
I thought I am Legend's ending was stupid.
I remembered what made me think of this thread... The ending to karate kid 2. He fights "to the death" with the antagonist in the whole movie, he wins the fight and asks him if he wants to live or die and the guy says "die" so danial-sahn says "wrong" and "honks" his nose like mr. miyagi did earlier in the movie. Who approved that ending, seriously?