This evening, I happened across one of the more useless varieties of "improve your accept rate" comments. Actually, that's all it was: "Improve your accept rate". I flagged the comment as "not constructive / off-topic" (I hate, hate, hate these kinds of comments. New users have no idea, on the whole, what to do with them. A comment with a link to a discussion on the topic, go here to learn more, or a little explanation in the comment itself, sure, but a bare four words... moving on).
I've seen these comments disappear when I've flagged like this before. Sometimes they don't - I figure there's a wording difference. This time, though, I saw something unexpected:
(that's not actually the comment I flagged initially. I went hunting for a comment without upvotes, in case that was contributing to the problem. It wasn't, apparently)
It sure looks like some part of SO seized on my flag and tried to delete the comment, but got hung up on something. The flag icon disappeared from that comment after that, and didn't reappear on refresh.
I hunted down another flag-worthy comment that didn't contain an accept-rate complaint (harder than I expected):
Flagging as "not constructive" worked just fine here, and as expected, the comment wasn't deleted.