To be an atheist means you don't believe in God. However, it is not an uncommon experience for us to be asked by Christians why we are angry with God. This can be a difficult question to address because it in a certain sense it doesn't make much sense at all, I don't believe in God, I truly don't think he exists, therefore I am not mad at him, it doesn't make sense for me to be mad at him.
I think one of the reasons for this confusion is that religious people, especially people who grew up in their religion, have a hard time imagining what it is like to not share their beliefs. They believe so strongly in God that it is pretty much unimaginable that someone doesn't. And so they conclude that I must also believe in God deep down I am just trying to deny it, I am so angry at God that I am choosing to ignore what is obviously true. Something along those lines.
Although I think there is some truth to that explanation, I was thinking about it this morning and it felt a little bit unsatisfying. There is a lot of anger among atheists, and it is often aimed at Christianity, is it really a surprise that sometimes Christians interpret this as anger at God? Furthermore, there was a period of time when I was angry at God. There was a period of time when I didn't consider myself a Christian anymore but I wouldn't call myself an atheist yet, I believed there was some kind of God and I thought he was an asshole. If someone knew me back then and heard me talking shit about God, and now heard me call myself an atheist, is it really that unreasonable for them to say "he's not really an atheist, he's just angry with God." They'd be wrong and if we had a conversation about it I'd be happy to clarify, but if we never talk about this specifically it would seem a reasonable conclusion for them to draw based on the evidence at their disposal.
Do I have a point here? I dunno, I guess it is to cut the theists some slack. Explain to them how their thinking is incorrect, but also understand that depending on their experience with atheists, it is perhaps not such an unreasonable conclusion to draw. Also, if you just assume that they think this because of my first explanation, aren't you doing the same thing to them that you are pissed at them for doing to you?