lawyer files complaint against women only wonder woman screenings

[gratuitous]

14. Businesses reserve the right to serve or refuse to serve anyone

The difference is whether the business holds itself out as offering service to anyone, but then changing its rules when someone comes in that they don't want to serve. But when the business openly advertises that it won't be serving (as in this case) men for one night, that's how it's different. It's how, for example, Curves "gets away" with being a workout center for women only.

Easy rule of thumb: If the business offers its service to the general public without reservation or restriction then decides not to serve you for a prohibited reason* after you've come through the door, it's unlawful discrimination. If the business tells you ahead of time not to patronize it for really any reason, it's in the clear.

*Obviously (though I feel it needs to be said in this instance) a prohibited reason doesn't include law-breaking or anti-social behavior (belligerent or violent or menacing patrons).