In an inexplicable twist of devilish fate, the person who you are having difficulties with approaches you and says the following:
You think that I don’t like you, that I am trying to sabotage you, and that I’m trying to turn others against you. Well, you’re right. That’s exactly what I’m trying to do. My reasons are my own, and it’s not worth going in to them because it won’t change my behavior at all. So I just wanted to let you know this and that and I’m not going to stop in the near future. Have a good one; I’m off to find other ways to make your life hell.
So there you go: your fears are confirmed. You’re right.