Its not illegal to have a private club with membership rules that exclude women. There are still several golf clubs that do so. In fact in the US its not even illegal to openly discriminate in hiring as long as the business has less 14 employees. In California that number goes down to 5 employees and local laws may be stricter still.
I mean sure it's illegal to exclude women but there are plenty of things they're just not going to show up to.
Want to be around only men? Go to a BSD meet up. (or join most channels on freenode.)
(note I'm not saying any of this is good, but there are plenty of places that are pretty exclusively attended by bales.)