Fans of the new G4 My Little Pony show "My Little Pony: Friendship is Magic". Mostly refers to the older male viewers of the show, but female fans use it too. A Brony is generally pretty involved in the community at large.
Brony 1: What's your favorite pony?
Brony 2: Fluttershy, cause she's just so cute!
Brony 3: Hey man, those are fighting words. Rarity is obviously the best pony!
Brony 2: What are you going to do?
Brony 3: I'm gonna love and tolerate the crap out of you.