But it isn't demeaning unless you (as the member of the group) take it to be! That's the whole point! Nobody ever means anything by it - that's why it's funny! It's just like when Newby calls someone a "nigger" - I think I can gauge his personality well enough to know that he doesn't mean it in the same way as I described in my post. A word isn't intrinsically "-ist" in any way - it's all about who's saying it and what they mean.
But it
is demeaning, because people
do mean something by it. I don't know what the proper name is, but I've heard it called passive racism. It's really the same as calling somebody a fag, which is passive gay bashing. For the joke to actually be understood, you have to understand that we're superior to women/black people/homosexuals in some way, so applying their traits to somebody is funny.
In other words, by saying that someone being a woman/black person/homosexual is bad, you're implying that those traits are bad, and, thus, it's racism, albeit passive.