A paper published in 2009 by some people I know contains the statement that it is problematic that a certain dataset does not exist because it would be really important to have such data but alas, such data have not been obtained, so instead they must use an ancient approximation based on a highly flawed technique.
I published just such a dataset in 2003 in a major journal, as the authors of the paper well know. One of the primary authors was a colleague of mine, although we stopped collaborating a while ago, by mutual agreement.
A few years ago, this former colleague asked me to remove his name from my research webpages because he was annoyed that my pages turned up before his in a Google search on his name. I did not think this was a reasonable request, though eventually the problem solved itself when I updated my pages to reflect new research and publications. Even so, I suppose this incident was sort of a clue that he might have some Issues.
Here is my internal debate with myself about the obvious non-citation incident:
Let it go. Their paper is lame and they undermine themselves by appearing ignorant of the literature.
Send them a passive-aggressive email with the relevant reprint attached, expressing regret at not sending the paper to them sooner, i.e. 6 years ago, and expressing surprise that they don't seem to have access to Major Journal, even though they do.
Let it go. Ignore them. Don't even admit that you read their paper.
And so on. Right now I am actually in a "Let it go. Ignore them." state of mind, but every once in a while I veer back to consideration of the insincere email/reprint option. I know I would gain nothing from contacting them and I would not feel good about it. So I won't do that, I think.
Why does it bother me that they did not cite my relevant paper? I am not upset that I lost a possible citation (really). I think I would be less bothered if they had simply left my paper out of a list of possible citations, but the overtness of the lack of citation was a bit shocking. That's what is so strange. And I suppose that is exactly why I should ignore them.
10 months ago