I find it hard to simply "hate" a person as a whole (not unless there's something particularly horrible they've done and their motives for doing so were utterly malicious and hateful in itself - I can't say i've ever had anything TRULY to that kind of extent in regards to people i've known/met directly in my life).
On average, it's usually the selfish reasoning (or lack of) including stubbornness or close-mindedness within a person that I hate more than anything else. One aspect of them hardly defines who they are as a person though so how can I hate them based off that? On the other hand it IS easier to perhaps hate or despise a particularly aspect or action from someone which then causes strong dislike for the person.
But personally I think the word hate is thrown around a bit too much (and is sometimes a 2 way problem) by most people in general. I could really only imagine actual hate for a person and everything that they are if they did something truly horrific. I'd say to me there's a line, and once that line is crossed, things like personal shortcomings etc that lead a person to do something becomes irrelevant and inexcusable (such as killing or seriously disfiguring/mutilating people) - I guess on that note one person (or people) i'd particularly hate is whoever carried out the Boston bombing(s) a few weeks back. That elicited a strong amount of hate despite my not even being an American or directly involved. Wanting to clearly inflict pain, suffering and take the lives of as many people as possible like that is certainly crossing a line no matter how personally messed up someone is or their shortcomings.