I'm very forgiving in this regard, as long as the movie is entertaining, I'll go along for the ride.

I did have a related weird thing happen once, though. I don't remember what movie I was watching, but about halfway through I suddenly realized everyone in the movie was acting and I couldn't watch anymore. It was a weird feeling, like they were all just lying to me, which of course they always are, but I was suddenly offended--"WTF? This is all bullshit!"

Maybe it was terrible chemistry. Maybe I subconsciously noticed all the subtle clues that the actors hated each other, but were pretending to be friends.

I suppose the one thing I can't forgive is a complete lack of chemistry between the actors, and that killing their performances.