Since one can't be snarky in a response to a review...

I'll do it here. I am currently revising a paper for resubmission. On the whole, the reviews are fairly reasonable, with the exception of one cranky comment from a reviewer who complains that our literature review is woefully incomplete. This incompleteness seems to be our failure to cite one particular study. The reviewer writes

It is possible that this work is flawed, but it really should be discussed.

It does seem to be a relevant study and we would have cited it, had we known about it. Why didn't we know about it? Because it has never been published. It hasn't even been presented at any of the normal psycholinguistics conferences (though it has appeared at some linguistics conferences). Short of emailing every researcher who might be conducting a study that might be relevant, I'm not sure what this reviewer was expecting of us.

I'd also love to know what the folks who are obsessed with only citing studies published in peer-reviewed journals would say. (It's possible that some of these conferences it has been presented at have pretty thorough review procedures; I wouldn't know.)