The question standing by itself has an easy enough answer. No. No one who can rightly be called an atheist can be angry at God (I assume we are all mature enough here to understand what I'm covering with the blanket term "God". For the sake of simplicity, let's take it to mean anything revered as higher than human, in the spiritual, and especially law-making, sense. That is different from revering the highest of man, such as with justice or truth.) So, we have covered that part. Simple enough.
However, I have noticed something in a few places that has really startled- I believe that is the right word- me. This angry type, the kind that goes on about the faults of God in a distinct way- that is, attacking those faults as one would with a person, not as in questioning why anyone would believe in a being with those faults, is definitely being incorrectly labeled. I believe most of us have seen the type I'm referring to. The railing against being judged, the complaints of all God has not done for him or her, the bitter demands for God to solve problems in the world. This person is obviously not an atheist. What has startled me, though, is hearing (or reading) these people called agnostics. This is, of course, completely wrong. These people are theists. They're not sitting side-by-side with those who subscribe to the infallibility of God, no, but they are just as purely theistic. Maybe even more so. They not only believe in God, but they expect this god to actually listen and pull through on some things. Being offended when something doesn't respond to you is a pretty clear indicator that you think it exists.
Now, I am not saying that anger about religious subjects automatically disqualifies an atheist. That's a view just as wrong, and somehow almost as common. There is no reason at all an atheist cannot be angry about religion. No one can deny that religions exist. Or, of course, some can, but that belongs to that philosophical school of thought in which the chair everyone in the room is looking at isn't really there. We'll have none of that here between us. I can understand how easily one can become upset by the various doctrines and dogmas and creeds. Despite the strong trend in world climate holding the opposite true, it is right to believe strongly. More than right. It is, one can safely say, essential to thinking beings.
As I've mentioned before, there are several common characteristics in religious people that I find difficult to connect with. In absolutely no way at all am I claiming that all religious people must share these traits. I'm only saying I have observed them often enough to forge a general concept of the various evidence. As a first example of something that angers me (and not a few other atheists I've known), we have the codes laced into religions which prey on weak people, including, but not limited to: recovering addicts, the recently widowed, the poor, the infirm, the mentally unstable, the mediocre. No, my dislike for the appeals to these people does not conflict with my personal responsibility credo. I am just as upset by the people who run to religion out of weakness, especially those who run in a moment of difficulty. I can at least respect when the religious decision is made with full mental clarity. No life-altering decisions should be made in the thick of stress and pain. Moving toward changes, yes, but, for instance, the decision to remain sober can only truly be made when one is sober.
The martyr complex is also repetitive enough to take note of, though this one certainly is not limited to any group. This little idiosyncrasy may just get to me more than any other- that obsessive need to take credit where it hasn't been earned, to take on tasks without being asked only to complain about how difficult it is to keep up with all the requests others make, and to go along with the decisions of others only to complain later about how dominating the decisive person is. As always, we'll have an example- introducing two people. This in no way gives the person doing the introducing a stake in all future interaction between the two introduced people. After the introduction, those two are free to act totally independently of the mutual friend, and so are free to accept the consequences of knowing one another in full. It's only one situation, but it is not hard at all to stretch it to fit so many.
I may seem to have wandered off topic, but I haven't. These two objects of anger I've listed are a way of showing, instead of just saying, that there is a huge difference between being angry at God and being angry at human institutions. I cannot- nor can any atheist or agnostic- have any feelings at all toward God, but those errors in human behavior- especially when codified into a ruling superiority for the sake of justification- well, it would be easier for me to believe them than to never take them to task.