Sometimes it’s really just someone having an off day and a gentle nudge will get them back on the path to greatness. It’s really easy to forget that text is hard to read (interpret) and people can misconstrue easily. So just give them that nice reminder.
If it happens again, or their reply is filled with expletives, they need to be forced to take a time-out. Once you’ve done that, it’s best to walk away from the situation, as you probably need a break!
On the forums, flag the post with the tag modlook and someone will come help.
On IRC, ask in #wordpress-sfd if someone with admin powers can come help. If no one is around, please email wp-forums and, if possible, link to the IRC log where it shows their behavior. They can be retroactively kickban’d.
Sometimes the users follow us home to complain. If they complain once, you can either reply or tell them “We prefer to have these communications on the forums, and ask you not email moderators unless they’ve explicitly asked you to do so.” At this point, if they’re being moderated, it’s okay to tell them that.
One email is fine. When they start badgering you, or if the email calls you names, we have a word for that: harassment
Ugly word. When that happens, block the user in your email. Yes, block. You are an unpaid volunteer, and no one deserves to be treated like that. Then email wp-forums about it, and someone will block the user.
We do not stand for abuse of any kind to anyone. And that includes you mods too.