Scott Pilgrim is an immature, self-centered little dork with the biggest case of literal main character syndrome. He’s a dick to everyone, and that includes being sexist. That’s the character, not the movie.

I understand your confusion though, because the entire narrative is built around Scott’s delusions. All of his insecurities and foolish notions are played out as if they are reality, because for the intent of this story as an internal reflection of Scott’s psyche, they are.