Why talk to someone just to be a dick?
'If you can't say something nice, don't say anything at all.'
Or, at the very least- If all you can say is mean shit, keep your fucking mouth closed.
There is literally no reason at all to speak to someone just to tell them you don't like them or you think their thoughts and opinions are invalid just because they aren't the same as yours. People are different from one another. They have varying interests and opinions and interpretations of the same person/situation/story/character/whatever. That is okay.
It is okay for people to like something you don't. It is okay for you to think they are crazy/wrong/stupid for doing so. It is not okay for you to attack them for it. Thinking nasty things about someone is okay. We all do it. Saying them to that person or even a third party just for the sake of being hurtful or trying to sway someone else into thinking the same nasty thoughts? Not okay.
To spew another cliche: Put yourself in their shoes. Would you like to have someone attacking the validity of your thoughts/opinions/feelings simply because their own are different? Of course not. Debate is one thing. Telling someone they aren't allowed to think something, that they're wrong because they aren't the same as you is just hateful bullying.