Assuming something isn't valid because it contains a fallacy is in and of itself a fallacy. Ad hominems are used all the time in extremely valid ways.

Take what he said in spirit, instead of literally.

It is invalid because the ad hominem is the entire content of the comment. There is no content other than the attack on HNers.

Well that's clearly false to everyone else, and again, is kind of irrelevant.

Nerds never seem to catch on that dismissing criticism as an ad-hominem is itself an ad-hominem.

I wouldn't necessarily say so. Rightfully pointing out that someone has made a statement which doesn't add anything to the discussion or support their argument is a valid counter to ad-hominem attacks which aren't automatically themselves ad-hominem.

Further, it's not an ad hominem to insult somebody while arguing with them. It's only an ad hominem if the insult is the basis of your argument.

The entire basis of the argument I am replying to is that people shouldn't be criticizing because "meanwhile back in their own lives, they still have to argue with project managers over the "right" way to get code done."

So that is the very definition of an ad hominem. The comment had no actual rebuttal to said 'shitting' that it was attacking.