Used frequently in New Orleans and maybe other places where people either A) have not learned proper use of prepositions or B) are speaking a version of English infused with constructs from other languages
pronounced 'by' but people spell it different ways: boi, biy, bi...and so on.
It is a term we cork (ireland) people use when referring to each other. It would be the equivalent of 'homeboy' or 'homie' and so on..!!