I am a very obsessive person when it comes to movies, TV shows, and characters that I like. If the topic comes up by chance, I want people to know it's an interest and a topic of knowledge. It's more or less complicated, I am self-conscious bringing it up because I know my ramblings will bore other people. If they come up naturally in conversation, I find excuses to ramble.
I buy merchandise relating to it, and draw a lot of fanart. When a fictional world has interesting lore, I like to delve down those types of rabbitholes too. Also topics that I find interesting like animals, biology, and cryptids. These interests and obsessions are a place where I can go to and escape from stressful situations in life. I get my hand on books with random factoids about said topics and read, and reread them. I read a lot about these topics and watch videos about them.
I find a way to associate every little random thing with what's on my mind, even if the connection makes no sense to an outsider. These connections aren't entirely intentional or conscious, but just how my weird mind operates. Once topics of interest come up in conversation I go on and on about them.