Humans have likes and dislikes.
Even with the same mammal, they want to hold kittens, but hippos don't want to hug them.
People who don't like hippos will think it's “annoying” even if a hippopotamus approaches you insistently saying, “Let's be nice.”
It's fine if butterflies come, but there are probably people who think it's annoying when flies fly in.
Even when it comes to humans, you may think “I don't want this person to get close” due to minor differences, such as the sense of distance when speaking or the way they speak, for example.
It's a crowded train, and I don't want to be approached by an annoying old man, but if it's a young kid, it's fine.
I don't know why (maybe there's no logical reason), but that person probably doesn't like you.
If you are approached by someone you don't like, they will show rejection.
In Buddhism, it is said that anyone can suffer from hate and hate. It's the pain of meeting someone you don't like.
It's a slightly different story, but there are food allergies, right?
There are people who show physical rejection (physiologically unreasonable) even to foods that are supposed to be beneficial to humans, such as wheat, eggs, and beans.
There are quite a few people who are allergic to eggs, and not that many people are allergic to wheat.
There are also people in the world who are allergic to you.
Maybe there's no reason.
However, realistically, when an allergen meets an allergic person, they are not happy.
Postscript 2/9
As you said, it's better to treat people you don't like with friendly language, love, and attitude of compassion.
Speaking ill of others is “evil” in terms of Buddhism.