It seems slightly indulgent to write an entire post on a single line of dialogue, well thats because it is. My bad. This line, although interchangeable between mediums, so it might read ' this is not a book, its real life' etc', has been making me cringe for so long something highly ineffectual needs to be done. AKA writing a post about it. Thats my justification, such as it is, so now I can get down to it.
1) its incredibly lazy, a go to platitude for writers who want to make it very, very clear that something is at stake in a scene, essentially saying this one's not like all those other movies. This ones' REAL. Then the comic relief gets eaten by athleticly adept zombies.
2) Stupid inter-contextuality. They know that we know its only a movie, so they essentially say well STFU this is real. No its not. Saying that come very closeto break the third wall, it has the opposite effect of the intended and makes us realise that it is a movie.
3) It hs never been delivered well. From Val Kilmer in Kiss, kiss, bang, bang to Matt Damon in the Bourne ultimatum, actors always always unconsciously express the thought 'man what a lame line' whether they mean to or not.
Writers, earn our interest don't try and distract us with bottom of the barrel tricks like this.