What are the two most important holes in a woman's body? No, it's not those you dirty bastards, it's her nostrils. They allow her to breathe while she is sucking your cock.
I don't get it. What's the joke here?
It seems like you are reading this joke wrong. A woman is supposed to breathe and be able to live through her nose. All holes don't matter to women and it's not sexist either.
It's not right to joke that women's only use is to be used as sex objects for men since that is a very dehumanizing perspective and will lead to discrimination against women. Women are people just like you and me and deserve to be valued for their accomplishments as individuals and not on their ability to provide sex. I think it would be good to consider how such views can hurt the women that you care about in your life and how it's better to be more positive and supportive instead.