I personally hate Gnostic Atheists...I can imagine everyone of them is smug. I'm stereotyping and generalizing..but I find absolutely 0 reason to be so certain that there is no god, when we have barely touched upon the mastering of knowledge.
Of course! While it's easy to suggest that religion was created for the sole purpose of finding explanations for things that we have no knowledge for, we still do not know absolutely everything. To claim with absolute certainty that we know anything is smug in its own right. Especially in religious terms, that's annoying.