Yes, it was Kyousuke who declared they hate each other, not Kirino. I'm very sure Kirino never hated him, probably quite the opposite even.
However, they never had much contact with each other. One reason for this could be that Kirino is quite good at school and sports, and thus probably got praised often by the parents, and got much attention by them. Kyousuke though, being more average, never got much attention. It could very well be that he always was envious of all the attention she got and thus started (consciously or unconsciously) to dislike her for it, treating her accordingly. Kirino then, angry at his unwarranted behaviour as she didn't do anything to him, starts to return it, and they start avoiding each other.
When their relationship picks up after he found out about her anime and eroge hobby, she doesn't know how to handle things.
This episode finally, she gets courageous enough to go on a date with him (using a yet-to-be-written novel as an excuse), hoping that he'll see that she does like him.
She starts off with a joke (getting hit by a car), but as she has a rather crude sense of humour, Kyousuke doesn't get it at all.
We can already see in the first half that she's got a crude sense of humour when she jokes about her friend Kuroneko being raped in her novel. Kuroneko has just the same crude sense of humour, joking about Kirino becoming a sex slave. While the two do differ quite a bit in some things, they also have more in common than either would ever care to admit.
After the joke didn't work, they go to a jeweller, and Kirino wants Kyousuke to buy jewelry, because she wants a present from someone she likes. This would've been an overly obvious clue for most already, but he's far too dense to get it
Nothing else she tries can get through to him either, so she finally pulls the stunt with the water bucket, trying to get his attention. They then end up in a love hotel - you can hardly get any more obvious than that. Kyousuke though, the king of the uber-dense, still doesn't get anything, and only gives off stupid remarks
Needless to say, that makes her angry. It would've made me angry as well
We already could see that he's the king of the dense in the first Manami episode when he didn't get any of Manami's advances, and later, over at Manami's house, he wasn't any better there.
In the end, Kirino hardly reached anything, and Kyousuke still has little idea about how she thinks about him. Even though he's that uber-dense though, his old dislike for her is crumbling ever more, leading to him defending her from her dad and Ayase, and now going out with her on a "research". Either he really was that uber-dense to not notice it was just a disguised date, where even Manami recognised it as such (wouldn't surprise me that much), or he's already liking her more than he would admit to anyone (including himself).