A combination of bro and Boba Fett.
It is used when a guy is referring to another one of his guy friends (one of his bros). It can be used at almost any time. It does not have to be used when talking about things having to do with Star Wars, although it will be better understood if your bros are familiar with Star Wars.
guy1: Hey bro, wanna hang outlater at my place with all the bros?
A lesbian bro. Mostly seen in flip flops, Abercombie, Hollister, polos, plaid shorts or cargo shorts. If she has long hair, it's usually slicked back in a tight ponytail paired with a headband/bandana. Can be seen at parties, sometimes in only a sports bra and jeans, doing kegstands, playing flip cup and/or funneling. Usually, as interesting as talking to a beige wall. Also see bro.
Girl #1: "Where are all the cute girls?"
Girl #2: "Clearly, not here. I swear, if one more brobian tells me about her flip cup tourney.."
Girl #1: "Yeah, not enough plaid shorts or polos in here."
Much like a broseph, a brobarian is equal to that of a bro, dude, man, etc. with the defining characteristics of being a rather large individual, usually quite muscular and strong, and being the friend that typically starts/finishes fights.
Jason: Dude, I wouldn't mess with Patrick if I were you, he's a fucking brobarian of mine.
Andy: Yeah, and what if I do mess with him?
PATRICK: I WILL FUCKING CRUSH YOUR FACE AND BEAT YOU WITH MY 5 IRON.