You can't comment like this on Hacker News, no matter what you're replying to. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.
I've replied to them too, but it takes at least two people to make a flamewar and you could have de-escalated or stopped replying at any time. Rather than pointing the finger at someone else, please make an effort to observe the guidelines and show you're sincere about using HN as intended. If you want others to be held to a high standard you need to hold yourself to a high standard.
The right thing to do if someone else is breaking the guidelines is flag their comments and email us at hn@ycombinator.com so we can take action.
By the way, you were right that the other person was inflammatory, and I should have called them out at the same time; it's just that we're often working quickly through lists of flagged comments and don't always think to look over the whole subthread.
In short, the answer to "why didn't you also call out that other user's abusive comment?" is almost always that we hadn't seen it yet, but we likely would have if you'd flagged it or emailed us.
You can't comment like this on Hacker News, no matter what you're replying to. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.