You should have known is an excuse for sexist incidents and a form of Victim blaming and Responsibility dodging where it is assumed that a woman should know (and accept) that, for instance, certain events or places are Boy's clubs, that a certain speaker or person is habitually sexist, or that certain comic or game is "supposed to have" borderline pornographic content. The argument shifts the responsibility to the woman, assuming not only that she is to blame for not knowing what would happen, but also chose in a way that allowed her to be offended.