It's important for channel and network operators to make sure those who want to participate in visible gender diversity on IRC are kept safe. This includes, but is not limited to, having rules and policies against mocking gender tags. It's also important not to push the gender tags on users: users may not be out everywhere and, by design, gender tags aren't channel-specific. Nevertheless, channel and network operators can - and should - do a lot to make more users feel safe to use gender tags.
Generally, if you mistakenly use the wrong pronouns, do not make a big deal of it. If it's on a post, edit the post to correct the pronouns. If it's an IRC message, and it's recent enough, correct it and move on. If it's a relatively old message, just use the correct pronouns for new messages.
If someone corrects you on their pronouns, responding with "d'oh, thanks" or "sorry, thanks" and moving on is more than enough. If you misgender someone in a private conversation they may not be aware of, do not message them to apologize about it. Chances are, they do not want to know.