It's easy to think cats are assholes when you project human behavior onto cats. Cats don't knock objects off of tables to be assholes, they probably don't even know what being an asshole means. Also, relating to the comment above, dogs are not good at consensual behavior or understanding a cat's body language when they are bothering the cat, so the cat may perceive the dog as a threat or nuisance, causing the cat to slap the dog.

I've had a cat now for about 7 years and before that I never really thought I would like cats. He's like a son to me and he is very sweet, but you have to understand his body language. Whenever I have visitors, I will let them know if he is not liking whatever they are doing, so that they can avoid getting slapped or bit. Cats are different than dogs in that way. Also, similar to people, cats have different levels of patience and every cat is different in this regard. Some cats will let you mess with them constantly, while other cats prefer having their own space and being handled on their own terms.