Someone who is a fan of both YouTube stars Tobuscus and PewDiePie. This term started circulating as a response to the trolls who were only a fan of one of the YouTubers; some of PewDie's fans ("bros") accused Tobuscus of copying PewDie because he played a few of the same games. In return, some of Toby's fans (the "Audience" -- the term "buscus" has been used recently as well) started accusing PewDie of copying Toby.
People who were fans of both started using the term "BroBuscus" to refer to themselves in an effort to show that there is no need for a war between fandoms.
Troll 1: OMFG TOBY IS TOTALLY COPYING PEWDIE I HAVE LOST ALL RESPECT FOR HIM WTF I'M UNSUBBING BECAUSE CLEARLY EVERYONE CARES ABOUT MY OPINION BECAUSE I'M SUPER IMPORTANT.
Troll 2: OMFG PEWDIE IS TOTALLY COPYING TOBY I HAVE LOST ALL RESPECT FOR HIM WTF I'M UNSUBBING BECAUSE CLEARLY EVERYONE CARES ABOUT MY OPINION BECAUSE I'M SUPER IMPORTANT.
BroBuscus: You guys are freaking idiots. Just because someone plays the same game as someone else doesn't mean they're copying that person.