Right now it's ROCH I'm reading, so...
So far I haven't encountered any character I'd downright *hate*...
Maybe Yang Guo before he grows up. Well, I'm no great fan of YG (though I may yet become one, haven't finished the book yet - and so far, he ain't half as annoying as the HXM version in ROCH 06)... But even if I do not really admire him, I can't say I hate him - except those first chapters when he's still little. I really really detest that child...:-)
I have a strong dislike for Guo Fu as well.
I may feel something like hate towards Zhao Zhijing - were it not for his having to deal with little Yang Guo. I can't help feeling sympathetic ever since then...;-) (I mean - imagine you'd have to teach the brat...;-))
But that's all just dislikes...
Nope. No such feelings as hate... Not yet.
There are actually some fairly unpopular characters I am deeply fond of...;-)
Now - Gu Long...
There were times when I really hated Lin Xian'er...
And I definitely kind of hated Shangguan Jinhong - though of course he was that kind of villain that commands respect...