$$$1.$$$ kursatbakis0 -600 Link
This post was initially about the fact that the comment author doesn't want to participate. The interesting part about this one is that no one down-voted it since it reached 600 down-votes 9 years ago. The post wasn't that bad actually, in my opinion. 
$$$2.$$$ rotavirus -581 Link
So close to the first place! This comment has no valuable information; it has bait for an up-vote and is not toxic, unlike the first place. Yet, I don't think it is truly one of the worst comments on Codeforces. 
$$$3.$$$ macaquedev -492 Link
The gap between 2nd and 3rd places is surprisingly big. This one is suggesting that a cheater was so good that maybe consider giving him an exception. While the idea has some ground to base on, the rating system makes it easy to have two accounts with semi-close rating. I shall remind you that Codeforces has single account policy. 
$$$4.$$$ Jamom -454 Link
This one was down-voted probably because it was political and quite off-topic. I also can see how it can be interpreted as being nationalistic. 
$$$5.$$$ KAN -449 Link
This one is really interesting; it comes from a contest organizer. Something really bad happened with Codeforces that round, and the queue of submissions was taking a long time to process. Some participants waited for 20+ minutes to see their verdicts. The status of the round wasn't clarified yet, and everyone was chill about it because they thought it would be unrated. Yet, this comment announced that the contest was changed to rated, and many people got mad because it really seems unfair. 
$$$6.$$$ nima10khodaveisi -445. A request for down-votes that worked
$$$7.$$$ the_xd -407. Victim of a comment chain
$$$8.$$$ sus -397. Also a victim of a comment chain
$$$9.$$$ codicon -395. The initializer of the comment chain
$$$10.$$$ nwatx -394. You wouldn't believe it, also a comment chain victim
