<p>A poster can delete their question if there isn't an upvoted answer.</p>
<p>You are entitled to feel irritated, even annoyed, if you answered the question, or regarded the question as good but made extensive comments, and then the OP deleted. But this is allowed behaviour. It's happened to me -- and to many others, I imagine.</p>
<p>Conversely, when comments run that a question is inappropriate or poor, it is often a good thing whenever an OP deletes the question.</p>
<p>Tags and kinds of question are immaterial here, but empirically it seems likelier that posters of self-study questions may wish to cover their tracks. Even if a poster is not identifiable by name, they may fear vigilance and be on dangerous ground given local policies on plagiarism or collusion, or may even be thinking competitively and desire to inhibit others finding out about a good answer. However, this is speculation and doesn't affect policy.</p>
<p>In terms of what you can do about it, I think the short answer is not much, but</p>
<ol>
<li><p>As here, Meta exists as a way to express frustration. (Over the years, I have come to value that greatly. The extent to which you will hear  &quot;I agree with you, and it's antisocial, but there you go&quot; is valuable mutual support. There are dozens of people active here who I have never met and in some cases they remain unidentifiable to me, but I have immense respect for all their work, including not only providing well-crafted answers but also voting, commenting and otherwise working to keep the site clean and tidy. That is the best of what a community means.)</p>
</li>
<li><p>Sometimes, posting a comment expressing frustration directly to the OP is tempting. The result can be anything from excellent -- someone realising that they shouldn't have done what they did -- to appalling, an almighty ding-dong in which offenders fight back in all sorts of ways, making nasty remarks or counter-accusations against you, even offsite as well as onsite, and mark you down long term as a personal enemy. I do not exaggerate.  Moderators tend not to like that, any way, and they are usually right.</p>
</li>
<li><p>If there appears to be a pattern so that someone is identifiably behaving badly and repeatedly, a custom flag to moderators may help.</p>
</li>
</ol>
