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I mean, it's just a cartoon, it's okay to be a fan and what not, maybe a normal brony. I can understand some bronies go full...creepy...serious business mode and eat, speak, and breath MLP...which gives bronies a bad name. I guess I'm considered a brony, but I don't go full what the fuck mode and become the stereotyped brony, and dedicate 100% of my posts to MLP references and be the only thing I talk about.
But if that's the only thing your friend talks about, then you need to confront him about it. Being a normal brony isn't bad, and by normal I mean just watching the episodes, check out fan art occasionally and read a fan-fic or two, have small discussions about it with others and what not. Not going over the edge and ONLY talking about MLP and fapping to its rule 34 and being male and over the age of 12 with MLP bedsheets. So ask him if you could talk about a different subject more often and not just....mlp.
Just remember, not all bronies are obese neckbeards who over hype themselves about a kid's show.