The Brony fandom is an infamous case of a male fandom for a girls’ programme but never the first. Their predecessors include Minky Momo fans, Kim Possible fans and Totally Spies fans. The latter in which involves strange obsessions, eerily predating what will become of the Brony fandom.
Likewise an earlier Pony fandom probably also did their own romantic fan fictions before Rule 34 was coined, held fansites and made pony versions of other, non-pony characters. Their idiocy was recorded early on Encyclopedia Dramatica, a few years before Friendship is Magic.
MLP had several animated productions before, especially in the 80s and early 1990s. The latter production had a cast that acted like the Mane Six in a way along with a de-emphasis on humans and an all-pony setting.
There were male fans before though many of them could’ve outgrown it for various reasons and watched those cartoons out of boredom. The contemporary Brony fandom peaked in the early 2010s, roughly 2012-2013 when it was picking up steam.
Of course, such mockery existed before but the current Brony fandom has become an easy laughingstock next to furries. In time, many might outgrow it but by then, it has little staying power.