My biggest turn off is when people do things way out of character or even against the physics of the plot just to create drama. It pretty much kills the movie for me because it is a house of cards and when it happens the structure of the movie is over.
One of the scenes like this that comes to mind is in Star Wars, I think Episode II, though I can't remember because I rarely watch I, II, or III at all.
When Amidala lands at Coruscant and an assisination attempt occures in the form of a bomb while they are coming down the gangplank. It turns out it was a decoy and when the real Amidala comes running to her aid, the decoy says "I have failed you" and then dies.
She didn't fail, how could she have failed? Her job was to take one for the team and she succeeded with flying colours. At that moment any possibility of me thinking that was a good movie was gone. Those movies are full of that mess.
Another one that makes me want to put my junk in a blender is in Hancock when the super lady is in the hospital bed and people are attacking. All Hancock has to do is get far away from her and the issue would have been resolved in seconds, he knew this by this time in the movie but he stays until we are treated to the scene when he is struggling on the highway to make .... the ... final... few ... steps ... and then she gets her powers back. It is a cheap way of getting tension and makes all their character building worthless because I am sitting there no longer part of the movie. Because the movie has gone full retard.