E. Ann Kaplan gives some insight to why sexism (or in this case, the representations of sexism) is not a zero sum game.
…two further elements enter in: to begin with, men do not simply look; their gaze carries with it the power of action and of possession that is lacking in the female gaze. Women receive and return a gaze, but cannot act on it. Second, the sexualization and objectification of women is not simply for the purposes of eroticism; from a psychoanalytic point of view, it is designed to annihilate the threat that women (as castrated, and possessing a sinister genital organ) poses.(emphasis mine)
Furthermore,
But psychoanalysts agree that, for whatever reason–the fear of castration (Freud), or the attempt to deny existence of the sinister female genital (Horney)–men endeavor to find the penis in women. Feminist film critics have seen this phenomenon (clinically known as fetishism) operating in the cinema; the camera (unconsciously) fetishizes the female form, rendering it phallus-like so as to mitigate woman’s threat. Men, that is, turn the represented figure itself into a fetish that it becomes reassuring rather than dangerous.”(emphasis mine)
Simply put, when women are portrayed as sexist on camera they have not escaped the male gaze as that their representation of sexism turns into a parody of the male position. By creating a parody of the male position they are given a false power that further trivializes them; this only serves to further ensure the male gaze.
There are many examples to show this in cinema. However, staying within the growing theme of this blog the ad below gives a quick concise example.
Steve Grimes is a graduate student at Brooklyn College and engrossed in cultural studies. He blogs at TimelyDonut.