Spiders. Yes, they eat bugs, but anything larger than the tip of my finger is not something I want very near me. They're perfectly fine out-of-doors. Indoors, no. Tarantulas are too big and hairy, but a nicer size to be caught and dealt with than smaller spiders.
Indoor insects. They belong outdoors.
Cockroaches. They are not good as pets, and are very likely pests. Plus, they're too resourceful for a pest animal. See squirrels.
Small dogs. They're too high-strung, generally, and loud. Exceptions that I like are mellow and not loud.
Creatures with squashed-looking faces. Ugly. Some people think it's "adorable". I suspect that the same people also collect the gawdawful useless ugly "collectibles" too, because they're so precious. My Quaker sensibilities are outraged. (My Quaker sensibilities are also squicked by collecting toys that no one's ever going to play with.)
Immature humans who can't grasp abstract concepts after they are concretely explained. Usually the threshold age for this is six/seven-ish.
Immature humans who don't recognize that "You don't think like me about this!" is not a crime against nature. Sure, it may make the person who thinks otherwise someone that you do not wish to socialize with, but it's not unnatural, generally speaking.
People who are abject slaves to the will of another outside of a safe/sane/consensual BDSM relationship. Been there, done that, burned the t-shirt.
Poisonous/venomous creatures. They and I can stay very far apart. Unless I learn how to handle them safely, I don't want them near me. I have no real wish to handle them in any case.
Ants. Especially the little biting kind. 'Co used to like eating carpenter ants. I used to take her to the anthill, and hold her above the trail, and she would peck up ants as they walked past. It was like an assembly line of snacks. I approve of chickens who like to eat ants. All the other hens thought she was a bit nuts, but there's no accounting for taste. Little biting ants in my kitchen aren't very welcome at all. Little biting ants in my bed are less welcome. I was trying to look up the journal entry about the biting ants in my bed, but Google is being less than helpful.