first time this came up at my house.. it was because of this video by TYT..
http://www.youtube.com/watch?v=3_FskEFU8ls1:10 a black women holding a knife with the caption "we're a culture not a costume"
1:15 a latino women smoking, pregnant, again.. with the caption "we're culture not a costume"
1:40 white men , beer belly, trailer trash looking hilbilly ... "we're a culture not a costume"...
i think this campaign actually defeats its own purpose..
I think the point there is that the stigma that is associated with each of those "races" is something that people of those backgrounds have to deal with on a daily basis. I.e. the black woman is saying that if you (or anyone) dress up as some "primitive" animalistic black woman with a knife, you can take the costume off, it's just a game to you, but you have then helped to perpetuate a certain stereotype about black women. And the latino woman is saying a similar thing. That the stereotypes perpetuated by people wearing these costumes are stereotypes that people of particular ethnic backgrounds have to confront on a daily basis.
It would be as if some white guys go dressed up as Arab men, in full abaya, flashing gold teeth, throwing fake money around at their belly dancer costumed girlfriends and underneath the abaya, have a "suicide vest" they keep flashing. Everybody at the party may laugh, but the arab guy (especially if let's say, he is an ex-muslim arab) there may not laugh as he has to deal with being stereotyped like this all the time.