Many Atheists Clearly Hate God. Why Is This?

If a person[b] truly[/b] believes that someone isn't real, then how is this even possible? I don't [i]hate[/i] any of the characters I've come across in fiction, even when within the story they've done horrendous things, because I know they don't actually exist, and so my hatred would be pointless and I'd only be making myself miserable for no reason whatsoever.
That being the case, who do so many atheists so clearly hate God? If He's not real, then... I'm sorry, but it makes zero sense to me!