People should be more open about it when they dislike someone. They usually hide it, though they may make unpleasant comments to the person or make a point of not being decent to them in certain ways. But they're usually very polite to them, which can make it harder to tell if a person *does* actually like you, or can lead to unpleasant situations where one party thinks there is a genuine friendship.
But not telling someone you dislike them also prevents criticism. You must have a reason to hate them, right? Perhaps you have a misconception. Maybe they don't realise they're being distasteful. It's possible that your ideas are wrong, and discussing it could reveal that, or that they're wrong and would be willing to change.
Or they could just be a dick. But there are solutions there too.
Not totally relevent, but still good.