If I'm a good person most of the time, but your mind tend to have evil thoughts that I never act upon, what does that mean?

Many people have these thoughts and they're normal.
Some even think of sticking a fork in their cat,but it passes quickly.
This is caused by a natural instinct of needing control and power
over others in life.

It means you're human. Thoughts are strange and varying.

You shouldn't worry. I believe its just what we do. We pick up on things (in movies, stories, etc.) and of course we will think of doing those things, without the intent of doing it. I think its when you actually see yourself doing one of those bad things is when it is getting weird.

Every one hes that, but not all act

It depends on if you're a care person or a fake care person. My dorm mate incollege was the latter. He really didn't give a crap about others unless it suited his needs but acted like he did. If you are that type of person, then you are likely a sociopath.

As for strange random thoughts that seem mean but you don't do anything remotely similar, you'r just day dreaming. In the case you are nice and do care about others, you probably just have a vivid imagination. You see sometimes we dream and daydream about things that we or others would never do. It's the brain's way of exposing you to the thought so that you won't do it or have the desire to.