Replace the gym with this cosmos and women with "mass". That means people in this cosmos have lost the contrast concept of "anti mass". They consider that all mass is positive.
In fact, negative mass does exist outside this cosmos. (analogy: that man outside the gym). It's something in the symmetric cosmos but not something that can occur in this cosmos.
Of course, we can't travel accross this cosmos and the symmetric cosmos to find out what's the physical property (identification property) between mass and "anti mass". That's why I don't replace the women with "particle". Because people find "chirality", etc, in this cosmos to distinguish "anti particle".