"Don't be snarky."

"Please don't sneer, including at the rest of the community."

"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize."

"Please don't post shallow dismissals, especially of other people's work."

"Please don't pick the most provocative thing in an article or post to complain about in the thread. Find something interesting to respond to instead."