Generally means the same this as Bitch Nigger but the first letters are reversed to make the phrase a little more white people friendly.
Me: "that guy has no game at all"
Tyler: Thats cause he's a Nitch Bigger
An alternative for "Bitch N*gger" for saying when black people are around.
Hey man... you are such a Bitch Ni.... (black dude walks over)... Nitch Bigger. Why did you steal my Charizard card?