I don’t think there’s a single catchall answer here, and a lot will depend on the circumstances of both the post and the reply. So for the sake of brevity, I’ll break down two possible scenarios:

We posted something off the mark that was maybe insensitive, or possibly excluded members of our community. Obviously we should always strive to avoid this, but this can and will happen from time to time. If we get called out for something like this, our instinct here should not be so much about ‘damage control’ as it is about offering an honest apology to our community members, offering a dialog about how we can be better, and also talking to our community about how we can pay that knowledge forward to communities adjacent to ours. We can change the mood by acknowledging that we were the ones that set the bad mood to begin with, and by being proactive in letting our community know that we aren’t cool with that.

In other cases, we might have somebody derail a topic that threatens to toss a post into the waters of oblivion. Maybe we have a troll, maybe somebody having a bad day, or maybe it’s an honest comment that just elicits bad responses. I think the first step is trying to identify the situation. Is it a troll? Is this a person that just wants to spread misery? In that case, it may be best to abandon ship on the post. Create new and exciting content that will get people talking, and encourage the conversation to continue there. There is nothing to be gained by engaging a troll. They have the advantage and trying to ‘one up’ them is just an exercise in absolute futility. If you have the feeling that it was less of a troll and more of an accidental post derail, you might be able to salvage the thread with additional humour. Don’t go about making the poster feel like they dropped the ball, if anything using self deprecating humour might help ease tensions a bit. Steering the conversation back to a place of possibility needs a gentle hand, and one that keeps the tone light. But like above, it’s important to read the room and know when its best to cut your losses and start anew.