I think it's reprehensible that parent has been downvoted. Ad hominem is ad hominem, no matter how deserving we think the target might be. Great-grandparent poster asked a question, ostensibly seeking an informative answer. What they got was grand-parent's uninformative tirade. While it certainly represents how people feel about Calcanis, it does not in any way answer great-grandparent's question, it is not informative, and it undermines the norm of civil discourse that we should expect on HN.
Ad hominem is not a synonym for insult. It is used exclusively for when someone attacks the speaker, and not the speaker's arguments. In this case, there were no arguments. The question was "Who is X?" Someone answered who X is. That answer was harsh, but also consistent with everything that I have seen.
I agree its civility is borderline. But it's not an ad hominem attack because no argument was being made.
Refresher: http://www.paulgraham.com/disagree.html