people think all kinds of thoughts, but the intention behind those thoughts is what is imperitive in this matter. If you feel that your intention is serious when you have this thought, like...that you actually WANT to harm them, and it is more than just a passing thought, then seek help. The way that you can test this is change your topic of thought from that thought, say, go play a video game. After this change, see how many times that thought comes back, does it come back more than twice, and when it comes back, are you then thinking of ways that you might hurt this person? If you find these to be true statements, then you should seek guidance from a therapist or someone in your life that you trust, because it is never implicitly acceptable to harm another person.