The Rule
In #xkcd (and #xkcd-signal), you may not act like an ass to women because they are women. You may not pepper them with obviously gender-prompted comments when they enter the channel. You may not joke "there are no women on the internet" or "pix plz" or "tits or gtfo." In light of how poorly women are treated in the geek/hacker communities in general, this behavior is unacceptable and will get you permanently banned from the channel on the first violation.
The other channel rules are generally up for discussion. This one is not. If you don't like this policy, #xkcd (or #xkcd-signal) is not the place for you.
 In Popular Culture
- XKCD comic #322