Well, the first line of the “In Comments” section is “Be kind. Don't be snarky. Converse curiously; don't cross-examine. Edit out swipes.” There's also: "Please don't fulminate. Please don't sneer”, “Eschew flamebait”, and “Please don't use Hacker News for political or ideological battle”.

It's common for people to not recognize that their commenting seems more escalatory when read by others than it does when it's being formulated in their mind, which is why we need to keep reminding people and asking people to make a conscious effort.