Most recently I'd have to say definitely The Last Airbender. I actually enjoy most of Shyamalan's movies (sans Lady in the Water, that one was seriously lacking in a good plot.) I had high hopes for Airbender, being a huge fan, and it was just dreadful. The only movie that beat Twilight in dreadfulness this summer, I think (sorry if people disagree but at least that movie didn't have focus problems.) On an older scale I would have to say Dragon Wars. I'm so disappointed that I will never get the money, time, or brain cells lost on those movies. I believe many can agree with me on those. While I'm at it, Forgetting Sarah Marshall and Knocked Up were terrible, terrible movies.