As a feminist, it is really frustrating to try to explain to people the way in which sexist ideology is part of so much of our lives. I'm Not Sexist, But website collects Facebook posts that use this exact phrase. Each individual post contains all sorts of problematic ideas, like implying that a woman's sexuality is morally wrong, that women are incompetent at their jobs, and that women's emotions are irrational or irritating. Collected together, this is a great site to point people to, since it shows the ways people are sexist in one of the forums that have become such a normal part of our modern lives.
The site also posts great feminist ideas every Friday, because not everyone is sexist.