When I find something I like, I have very few qualms about letting people know I like it. Same goes for MLP.
I was first introduced to it by Shael Riley, who if you are not familiar with his music, go and check it out. It is really good chiptune alternative music (I know, what does alternative even mean these days?): https://shaelriley.bandcamp.com/
Anyway, he and and a nerdcore rapper called Beefy did a podcast of miscallaneous songs, each one of them picking a track in tandem. And one of Shael's picks was the Alex S. remix of the Cutie Mark Crusaders song. I loved it! After the song finished playing Shael explains to Beefy about how he was introduced to the show and his thoughts on it, and just his description made me think "alright... a show whose target audience is young girls is being enjoyed by grown men?!" It was just too weird, so naturally I had to check it out.
I watched the first episode... and then the second... and third... and nth... all the way to the end of the first season. I was hooked! And then I had to wait almost 6 months for season 2. So I would say I declared myself a brony after the first two episodes.