A friend of a friend, coined from the word 'bro' and the 'in-law' suffix given to people where you have a connection reliant on another person.
Person A: Yo, Person B, I heard you have a bro-in-law with someone.
Person B: Sup Person A, I have multiple bro-in-laws.
Person A: Like who?
Person B: Person C, Person D and even Person E are all my bro-in-laws, all linked to Person F.
Person A: Kick-ass.
Your friends friend, basically a mutual but who the fuck wants to say that when you can say “Bro-In-Law”.
Guy 1: Yeah I had no clue who he was, but I dapped him up anyway because he was my Bro-In-Law.
Guy 2: What the hell is a Bro-In-Law?
Guy 1: it’s your friends buddy you don’t know.
Guy 2: oh so like a mutual?
Guy 1: i guess so
This is one of your girlfriend or wife's sister or sisters. This relationship is one that is contextualized by using fratty language, such as referring to each other as "bro" and using the word "hella" frequently as an adjective in encounters where both parties are involved. The chick-bro-in-law makes your relationship a packaged deal.
Michael: "Hey bro you wanna hit the club up tonight?"
Joel: "No bro I'm getting hella drunk with my girl and chick-bro-in-law tonight, at this fancy restaurant. It's gonna be so bromantic."