My least favorite—and all too popular—comment is the classic "How [or Why] did this make the front page of HN?" I have gotten to the point where I almost expect to see it near the top of every comments thread.

In fairness, the HN guidelines are pretty clear about this one:

Please don't submit comments complaining that a submission is inappropriate for the site. If you think something is spam or offtopic, flag it by going to its page and clicking on the "flag" link. (Not all users will see this; there is a karma threshold.) If you flag something, please don't also comment that you did.