I became a brony sometime in April last year (2013), I think. I was aware of the existence of MLP FiM and bronies a long time before that though. So, I'm in this web forum called MGS Forums, and I'm invited to join a certain Organization within that forum and I accepted their invitation, because they seemed cool.
This is when the process began. I couldn't help but notice the Pinkie Pie graphics of a certain member. I had seen bronies in other places in the internet before, like Youtube, but I've never really tried to talk with one. I asked, "What's with the pink pony, dude?" He replied, "Oh, it's from MLP FiM, it's a great show" then I said "Yes, I know about the show, I just don't get this 'phenomenon involving it. It's just a regular cartoon to me. A cartoon made for little girls for that matter". And the discussion went on and on, he even teased me, saying that he could make me a pony signature. In the end, he didn't convince me to watch the show, but I didn't judge him for the fact that he watches cartoon ponies, 'cuz he's a great guy.
A few weeks later, a friend of mine invited me to watch a movie in the theatre. I agreed and went to watch it. So, we got to our seats kinda early, so I got my iPhone and started browsing the internet a little. I then went to that forum to check if there was any new posts in some threads. That guy with the Pinkie graphics posts there everytime. When my friend spotted his images, his brony switch turned on. "DUDE!! I DIDN'T KNOW YOU WATCHED MLP!!" "What? No, this isn't me, it's a friend of mine in the internet" I knew this guys since I started High School and I never had any idea that he was a brony. That made me curious. "Wait a second. You watch this show too?" "YES, YES, I know what you might be thinking, but it's a great show!!" And we talked about it until the film started and interrupted our conversation. We didn't touch the subject again. But my curiosity grew even larger. I know two guys who watch this thing. They both say it's awesome. Hmm...
A week later, my friend spots me on Facebook. We start talking about stuff, until he asks if I watched the show. I said "No." "C'mon dude! Just give it a chance!". I was actually very curious about MLP, but I couldn't tell him that, could I? XD I just said "Maybe". After that small conversation ended, I went to the forum to ask that Pinkie guy where to start watching it. Let's just say he was quite please with my question, to say the least XD. He told me to just watch them on Youtube.
So, I went to YT and searched for "my little pony season 1 episode 1" and watched the first premiere. It wasn't that bad. I put another episode. And another. And another. And another. By the time I stopped watching it I already reached "Fall Weather Friends". Yup, I was hooked.
And there you go. How I became a brony.
tl;dr version:
Two guys tell me ponies are awesome.
"Meh, okay"
*watches MLP*
"THIS THING IS AWESOME!!"