This means to dismiss an argument because it’s associated with a certain group or stereotype, rather than the correct way to dismiss (or accept) an argument, which is reason! One obvious example is discussing any kind of argument that suggests that men are actually not advantaged, which can be immediately dismissed as ‘incel’ rather than discussed. Conversely, it could be freeing and helpful to consider some issue in terms of patriarchy, but then this is immediately dismissed as feminist BS, rather than reasoned.
Sometimes you are the stereotype. People can dismiss what you are saying because “you are one of the __________ types” [insert relevant blank].