The morally (and socially) appropriate thing to do at this point would be to apologize and pledge not to use that kind of language on IRC in the future, rather than saying "Hey, I don't do it that often" and subtly digging at startling for publishing your abhorrent comments.
It's not clear to me this is the case. It was inappropriate to publish the logs publicly, rather than pursuing a private resolution (by messaging gwern, a moderator of the channel, or so on) or asking about the issue in general terms, and seems generally unhelpful to claim that gwern intended to provoke the author of the great-great-grandparent.
I agree with you that now that the logs have been published, apologizing and pledging is more transfriendly than not, but it may be better for gwern's reputation in general to point out that this is an isolated incident, rather than a trend (which apologizing is evidence for). I should note that the question of whether or not to apologize and the question of whether or not to publish logs are distinct, and that I am unsure about the right choice for gwern on the first (but would personally apologize) and agree with him on the second.
I suspect a contributor to this issue may have been that a new user was unsure how to deal with an established user; it may be useful to have an advertised ombudsman. To back up that suggestion with action, I'll commit now to taking seriously the concerns any user would like to privately raise with the behavior of another LW user.
I appreciate the ombudsman sentiment -- it certainly would have helped if something like that had existed.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.