How do you deal with people who hate you for no apparent reason?

I tend to ignore these kinds of people, not care at all, and usually the feeling of “Not them again…” is mutual. But every once in a while I stumble upon someone I like/respect who either outright hates me or ignores me for the most part. I am far from being a people pleaser, though I would kill for the ability to read people’s minds and see why they are being this way. Why do people do that? How do you deal with people who “actively don’t care” about you no matter what you do?