I don't think comments like "you use X in model solution, author, are you an idiot?", "f**k you and your problems, they are shit" and such should be normal on Codeforces, especially when written by someone high-rated and/or respected in the community. I also don't think this kind of behavior should be normal towards regular users.
I know that sometimes contests can be frustrating. Sometimes it is the participant's fault, sometimes it is the problemsetter's fault, sometimes it just happens without anyone being guilty of that. And I understand that in some cases, the criticism the author receives is fair and well-deserved.
But there is a fine line between criticism, saying that you didn't like the problems, and hurling insults against the author. The former two are acceptable (and sometimes even needed, because authors have to improve and learn from their mistakes); the latter one, in my opinion, should not be acceptable.
It's not like we can ever get rid of offense and hatred completely; there will always be people who want to take it out on the community as a whole or someone specific. And if I created a blog for every time I saw an insult hurled towards me or some other member of the community, my account would already be banned for spamming. But I think that the comments like the one linked in the first paragraph are especially dangerous and need to be dealt with.
Codeforces community is biased towards people with high rating and people who do something for the website. And this is sometimes a good thing; but it can also make people think that if a high-rated participant and a problemsetter allows himself (or herself) to be rude and offensive, then it is acceptable, and they are allowed to do it as well. That's why cases like this one are especially bad.
We can never get rid of offense and hatred, but please don't make it something normal. Everyone should be responsible for what they are saying or writing, but if your word has some weight in the community, then it also means some additional responsibility for you. Please don't make people think that insulting the author (or anyone else, for that matter!) is perfectly reasonable and fine — I doubt you will like the results of that.
UPD: It looks like the focus of the comment section has shifted towards discussing how to give constructive feedback to the problemsetters. This is certainly one of the points of the blog, but the main thing I wanted to state was that insults against anyone should not be acceptable. It's just that the problemsetters usually get the most of the hatred on CF, so it's much easier to find the examples of that. But this behavior towards regular users should not be allowed either.
UPD2: Initially, there was a link to the comment which caused me to write this whole blog (a comment by a high-rated user and a problemsetter when he openly called another problemsetter retarded because of some details of the solution). I wanted to show it as a clear example, but it was not the right thing to do.
To the person whose comment I used as an example (if you're reading this): I apologize, I shouldn't have made it seem like you're the culprit, and I didn't understand the consequences of my blog fully. I know that you have openly admitted your mistake, and I admire you for that. If the fact that I've used you as an example made you feel awful, or made some other people call you out — I am terribly sorry.
