It was pg's coinage, but I don't know where he first used it. https://news.ycombinator.com/item?id=4693920 was the first time on HN, a few weeks before the link you mention. I think he might have introduced it in an essay before that, though.
We use the term 'shallow dismissal' in HN moderation instead—arguably a bit of a euphemistic move, but for moderation purposes it's a lot better to talk about the post than about the person. The word 'shallow' makes that clearer than the word 'middlebrow' does.
We use the term 'shallow dismissal' in HN moderation instead—arguably a bit of a euphemistic move, but for moderation purposes it's a lot better to talk about the post than about the person. The word 'shallow' makes that clearer than the word 'middlebrow' does.