In a group of individuals (a 'population') in which particular gender stereotypes prevail, even those individuals who don't believe in those stereotypes would find themselves acting in accordance with them. The reason: Stereotypes may be wrong, but they are a very efficient way of social dealing.
Consider a crude example. A college in which there is gender segregation to the extent that it doesn't abolish all interaction, but the slightest deviation from academic discourse is met with the suspicions of flirtation. We have a boy X and a girl Y. Since the stereotype is so prevalent, it is natural for X to assume that Y is a typical, conservative girl, and it is natural for Y to assume that X is a typical boy with no other intention than to make a pass at her, when in reality (in this case), both X and Y don't believe in these stereotypes and behave in very different ways when they meet with members of other populations where this stereotype is not present. For X, if he doesn't behave in the limits set by the stereotype, he has the risk of being misjudged as a flirt. For Y, if she doesn't assume X to be a flirt on an occasion of interaction between them, she has the risk of X actually being a flirt and being 'misused' by him. The risk forces both X and Y to make the assumptions which propagate the stereotypes. Stereotypes sustain themselves by posing a risk against those who don't believe in them.
For that stereotype to disintegrate in that population, there would have to be a first few casualities. X would have to make the assumption that Y is not a typical, conservative girl. Y would have to make the assumption that X is not a flirt. They would be misjudged, most probably; they would become casualities. But if they persist in their attempt to not see others through the lens of stereotypes, soon other individuals of that population who are only acting on stereotypes to be safe would start following their example, and the hold of stereotypes would break. Every liberty needs its martyrs.