One word... sexist. It would be called sexist. While I'm totally pro female, exclusivity is still bigotry no matter how you look at it.
I supposed girls nights out are now sexist as well, or just chilling with the guys and no girls.
How far will it go?
Once you start to give one group preferential treatment based on their gender, that's sexism. There's a difference between the -ist and the -ism, but it's an important one :)