Slang for the term "brotherfucker," meaning one who has sex with their own brother. This type of incestor is probably breaking the law in some way and/or will have deformed babies.
Person A: "Daaamn son, Jake's sister is a brotherfucker
Person B: "Say what? That word is too hard to understand."
A: "How about brofo
B: "Too short. I don't get it."
A: "She's a.... bruthafucka?"
B: "That's it, man! That ho is one who has sex with their brother if I ever saw one! A straight up bruthafucka."