Was there something wrong with my original post? (I understand that responding to flamebait may have been a mistake.) I was legitimately trying to add to the discussion. And from what I've seen on HN, I didn't think there was a particular ruling towards manners in posts. Would it have been more appropriate to etiquette if I'd been less emotional in my post?

Yes. As it says in the site guidelines, the test is whether you'd say the same thing face to face. I hope you wouldn't say "if you say otherwise you are a stupid, ignorant fuck" to someone's face.

It depends on the situation.

I don't see Hacker News as a formalized discussion area. People congratulating each other and joking with each other tend to be observable in several places. This is a place for smart discussion, yes, but not necessarily formal discussion.

Given that, then yes. I would absolutely say a line like that, expecting people listening in to understand that it's a piece of hyperbole rather than an actual belief. The fact that I then responded rationally when the OP replied should show that, in fact, I don't hold him in any sort of contempt. And, if I was in a setting with reasonably bright people having a conversation, I would use the phrase "stupid, ignorant fuck." The language alone should have made it obvious that I was being hyperbolic to attempt a point of debate.

I guess that's not how you see it, though, so I'll avoid any sort of dialect like that in the future.