This is a difficult issue to address, and while I think most people on the thread have the right motive, I don't think they realise the implications of what the OP said. Now I'm not an expert on this, but I know people who are, so I think I can help clear up some things (and if not I'll get them to join and post).
Wanting people to be treated equally is generally the right thing to do, but think about this: in some of the examples above, it was said that everyone treated each other the same until someone mentioned they were female. So should people not mention their gender? Then everyone gets treated equally, because they are all assumed to be male, which is NOT the right way to do it.
What should really be happening is that people should be able to mention or not mention whatever they want about themselves, and it making no difference at all. People taking advantage of attention on the internet isn't helping, but blaming them for causing the attention is incorrect. If someone pulls a gun and shoots someone else, do you blame the victim for being in the path of the bullet? Even if they want to be shot (okay, not a great analogy - insurance fraud, maybe?), it's not their fault the shooter pulled the trigger.
So yes, even by listening to the OP, you are still being sexist, even if you do not realise it. Like I said, I imagine they had the best intentions behind it, but it is a difficult issue, and sometimes the best intentions can do more harm than good. (I am not even sure if this post is the best thing to do, but I feel I should at least try.)
I would hope that most people on here do not need this advice, but my suggestion to reducing this as an issue would be to not react to people's usernames. If someone is clearly trying to get attention then obviously ignore them, as they are only making things worse, but otherwise just try and react normally whilst bearing in mind that everyone you ever meet online could be of any gender, any sexuality, any race or nationality, etc. Don't just treat them as a guy - treat them as someone who's gender could be anything at all, and remember that whichever it is should make no difference whatsoever.
I would rather not mention my gender in this post, but since I am capable of mistakes and badly-worded arguements I feel I should say that I am a guy, and if there is something sexist about my post that I have missed or misunderstood, I would like to be corrected on it.
EDIT: Just while I'm on the subject, has anyone else noticed that my current rank is paperboy? It's hardly the biggest of mysoginistic crimes, but it only helps spread the myth that only guys exist on the internet...