My opinion of "Worst Movie Ever" changes constantly. Right now its stuck on The Last Airbender. IN MY OPINION (note the opinion part) its worse than Twilight Saga or Transformers.
Why? I never had expectations for Twilight other than "blow massive chunks" and I'm not a Transformers fan so I just watched it to see massive robots beat the oil out of each other.
As for Airbender, I'm a MASSIVE fan, so it hurts to see and hear it being shredded apart like this. A bit of me died every time someone mispronounced "Sokka" and "Aang", the bending looked weird, the casting was... ugh. The movie already suffers from a lack of Mako, no need to shoot yourself in the foot any more (or blow the entire foot off).