How to Nerd Like an Adult 101 - Part 1:
It's okay to let people like things. Even things you don't like. And it's more than okay to let them like things you don't like without telling them you don't also share that enthusiasm.
Because when people talk about the things they love, they are looking to make connections with other people who love things, not to be told they are wrong or foolish for liking the things they do.
Before deciding to chime in a conversation between enthusiastic people talking about the thing they enjoy, be it sports, a given kind of music, a TV show or a game, ask yourself this:
Is what they like harmful? If yes, are you sure? Not harmful to your conception of good or bad but actually perpetuating some immediate social, physical or mental evil?
Unless the people in question are grooving on stabbing other people, some kind of shaming or being otherwise cruel to others, the answer to that is almost always 'No'.
You're a grown up. You have the capacity to judge between 'distasteful to me' and 'actually harmful'. Use it.
And if the answer is 'no', then I propose something that nobody ever tells anybody in the geek world or the Internet in general. Just shut up. Deal with it. Walk away and talk to people about the stuff you like. Or leave that online conversation alone.
Because I assure you, nobody who is having fun talking about the thing they love cares you don't like it just as a matter of personal taste. And you can only annoy them and make yourself look like a jerk (because, you know, you're being a jerk) by making sure that the conversation is turned to how much you hate whatever it is they like.