Quote from : Excluded: Making Feminist and Queer Movements More Inclusive Book

Sexism occurs when we assume that some people are less valid or natural than others because of their sex, gender, or sexuality; it occurs when we project our own expectations and assumptions about sex, gender, and sexuality onto other people, and police their behaviors accordingly; it occurs when we reduce another person to their sex, gender, or sexuality rather than seeing them as a whole, legitimate person. That is sexism. And a person is a legitimate feminist when they have made a commitment to challenging sexist double standards wherever and whenever they arise. An individual's personal style, mannerisms, identity, consensual sexual partners, and live choices simply shouldn't factor into it.