I probably started becoming a brony at halfway 2011 or something, but when I became a brony I remember that all of the season 1 episodes were out by the time I finished watching them, and the 1st episode had 1 million views before it was removed...
I was introduced by a friend in a chatroom at a gaming site during the first days of summer vacation,sent a link and told me and a couple other buds to watch it. I was in the living room, luckily by myself there, because when I clicked on it my mind starting thinking: "What the heck am I watching? Am I really watching a show about ponies?" And sat down through the whole episode, at parts thinking why am I still watching this, and secretly starting to like it!? By the end of the first 2 pilot episodes, I was hooked, yet ashamed I liked this show, not realizing how popular it was and the fans(and their fanon name.) No less than at least 2-3 days later, I discovered Equestria Daily (EqD), and secretly started going to it and enjoying its posts, learning about the large fandom and their name.
Bronies. --How I became a brony stops here.-- Continue to read to find out how I discovered EO(Which eventually seperated into LoE.) If you actually care.
Soon I learned about Equestria Online (The Pony MMO Project, I call it at times) and never felt so excited that a Pony MMO was being made, and hanged out in the suggestion part of the forums, giving ideas. Never said hello in the Introduction Threads. A week or two later had the guts to click on the IRC, before thinking it was for team members only, and then ended there is the IRC, going there and the forums for months and BLAHBLAHBLAH. At this point you probably really don't care.
TL;DR: I became a brony from a friend at a gaming website.