Couldn't the same be said about posts that even are on topic? Like, no ones opinion about Black Panthers box office matters either
I mean, if you want to take it far enough, most things you do in life are meaningless. But since we've all agreed to spend some of our time on a forum, part of the also agreed upon social contract is that you discuss the topic of a thread. Some people, however, consider their extraneous and tangential opinions so valuable and necessary that they must be shared in a thread that isn't really about that. I would say the ego required to think your opinion or taste is somehow required and helpful context to understand something as complex as "harassment is bad" or "wow, that sure is a successful box office" is more conceited than engaging in the standard social mores.
Again, we could be talking about how harassment functions on the internet, but mostly people are talking about how they felt about a movie and then saying that adds context. What context? What value? It doesn't change their opinion or behavior. It's just extraneous information. People just want to use anecdotal details to make their post feel like it adds more. It doesn't, though.
I don't see a clear division between box office and quality as topics for discussion. One easily bleeds into the other.
I also can't see it as conceitedness. In the context of a discussion forum, folks are invited and encouraged to share their perspectives and to put thought into what they're saying (i.e. to believe that their opinion or perspective matters). To then call them conceited feels at odds with what a discussion forum asks of you.
I would love more posts in this thread to be people sharing their perspective on harassment faced by women of color in nerd spaces and not their perspective on a movie that has been discussed to death.