Moral or not
I think you know when you cross that line. You feel sick and odd sitting in movies that don't fit your standards.
For example, me, my brother, and my sister all went to see Distrubia one night. I remember that I wanted to see it because I had never seen a horror movie before. There was appearently a reason for that. Sure it was fun right when I came out of the theater, but the next day was misery. Images and lines that kept entering my min,. It took a year for all of those to go away.

That is not to say I don't watch movies with violence. I loved Dark knight. That one was scary, but it wasn't the sensless bloody gore that disturbia was. It talked about real moral delema's and truths. Through the whole movie I was thinking. "Was that the right choice, if so why?". I'm still not completely sure what I think, but it was was a powerful movie.

So I suppose that kind of goes with movies lying to you. I don't like to see things that are wrong and sad as fun and care free. It just makes the whole movie seem minipulative and fake.

I guess ultimetly I'm still undecided. I could name a list of movies I aprove or dissaprove of but I'm not sure I have any set rules about how to tell if somethings apropriete or not. I only know that if I feel like its not right, than I shouldn't watch it.