Sure, the question is sometimes trivial. But it's also a question that keeps us on our toes. I run a secular student organization - atheist, agnostic, secular humanist, pro-free speech, establishment clause, all that and so on. Our group is largely feminist, but for years suffered a severely lopsided gender disparity.
We ask ourselves "is it sexist?" because sometimes things that seem so obviously, ordinarily not-sexist, like a self-ascribed title, can result in a sexist impact. Some atheist student organizations I've met across the country allow personalized titles. I've met people who described their position in the organization as "Batman", or "God". These titles send signals that the group isn't serious.
Completely innocuous, non-sexist things can send entirely sexist signals. The types of events a student organization advertises: board games versus video games, can result in huge gender disparities. Catering to one because your current members prefer it is not sexist. Catering to one and ignoring the impact it has, is.
I think to be a proactive feminist, you have to examine the total impact of your actions, not just what individuals intended to happen. You have to examine not just why a decision was made, but what factors weren't considered in making it.
Is Parisa Tabriz sexist? No, I don't think so. Is she a bad feminist? I couldn't even begin to answer that question, I don't know her.
But is her title sexist? I have to think of my student organization and the signals we send. If my Director of Membership asked to change her title to "Membership Princess", I would say no. That sends the wrong signal to potential members.