How would you define the difference?

Sarcasm is writing the opposite of what you mean. It doesn't work in short form text (similar to Poe's Law) but people do it anyway because it works in their internal monologue that has vocal intonation. Even when it works, it's an obnoxious outburst and intellectually devoid of value.

Snark is general obnoxiousness that adds no intellectual value.

It’s not to signify a difference, but to expand coverage. I wouldn’t want to argue with someone saying “I was sarcastic, but not snarky”.

There are many comments ending with /s to signify sarcasm or even /sarcasm or such. It’s easier to point out a transgression when the user has agreed in his mind or his words that he was in fact being sarcastic.

I think we'd just reply that they're close enough to count as the same thing for HN purposes. "Don't be snarky" is nice and short.

It’s not so much for you as it is for me. I often quote the rules, this would make it easier for me.

Ah I see. If it comes up, you can point to this subthread, or you can always ping us at hn@ycombinator.com. Thanks for quoting the rules and helping to preserve this place!