So are you asking if it is OK to tell someone you hate them? I actually don't think I would do it even if it is true. Recently, I've had more interaction with my brother than usual (he has been living far away so I don't see him often). I have become more aware of my feelings, in general, from having worked on recognizing my feelings in therapy. I've become aware I just don't like my brother. I don't like who he is and realize he rubs me the wrong way a lot of the time, just by being who he is. I don't think I will tell him I don't like him. I will just try to minimize our interactions and not initiate contact. If I need to be around him, I will give him opportunity to surprise me and be different, i.e. I won't shut the door. It's not like I can tell him hey when you do such and such, it bugs me, could you stop that? Because it's a more global problem than that. It's who he is, not just something here or there that he does. It kind of feels good to know this is how I feel about him. It allows me to set better boundaries for our interactions. I don't need to tell him I don't like him, though. But I also won't lie to him and say I like you, you're wonderful, etc.

That's my approach, anyway!