No matter how "messed up" your inner fantasy may appear to be, there is nothing wrong with it as long as you don't let it affect reality.

I've had similar experiences myself when dealing with people who upset me. When talking to these kind of people I've actually had fight scenes play in my head with me killing them in several different ways. I don't let it effect me negatively in my interpersonal life and it helps me cope ,therefore, I don't see a problem with it.