I actually find hostile characters almost every single time I’m about to become lucid. I’m still kind of noob at this, so I think that may be part of the reason, but it has become odd by now. The degree of hostility is very variable: sometimes, they just want me to keep doing what I was doing before my reality check (“hey, we’ve got to keep pouring the blue substance through the tubes, you can do that later!!!”); some others, they assault me in a friendly way (a pretty girl in a dream I had last week just started kissing me); others they will just attack me with whatever they have at hand (a midget who decided to jump and scratch my face, and another dream in which a mob at a restaurant started poking me with forks); and finally, the ones that really don’t want me there (they actually called down a tornado while I was doing my reality check ).
I do agree that having them hostile at sight is part of the movie plot; however, I think that point is actually based on the fact that sometimes (or in my case, almost every time), dreams just want you to be clueless about you dreaming.