My guess is that the cashier ham associates Women's clothes with plus size/fat clothes, because in some stores they do market "Women's" section within the Woman's section as the fat people's area (so instead of using the label "plus size", these stores will use the label "women's size"). It's dumb but I guess these stores do it so as not to hurt ham feelings. Fatso is too dumb to realize other women sizes exist than the tents she regularly buys.