Anything that takes you out of a book, film or tv show by exposing the creative process.
In old movies where you could literally see the string holding people up, you would be taken out of the film because you could see the method of creating the effect, and be reminded you were watching a movie. Examples could also include speech making in books and films, where the characters are spouting the writer's philosophy, or going into expositional dialogue.
That speech just ruined it for me; I could see the strings.
That lazy coincidence took me out of the story completely - I hate it when I can see the strings.