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.