It's the claws, litter box, sneakiness, the dead animals at the door step. They remind me of dirty rodents and it tickles when they walk on me. Then it hurts when they claw me cause they startled me and I move to quickly. They don't really listen either.
Cats are nice little companions to have if you want someone to sit on your lap and relax with or watch their silly little antics. However Dogs generally have more likable traits like obedience and are easier to train. Most people hate cats simply because they compare them to dogs. I prefer dogs, but I enjoy a nice purring kitty on my lap too!
I really don't think everyone hates Cats. I made a comment once about the way a Cat is and the girl just came unhinged! They are what they are, and they do not need their pet owners as much as the owner needs them. Cats are just like that.