little brown book 

a small notebook or document in which an individual keeps a running list of the names and phone numbers of people they have had anal sex with.

bro 1: "hey man, do you have that Puertorrican midget's number?
bro 2: "yeah it's in my little brown book, let me get it"
(bro 2 pulls out LBB)
bro 1: damn, that thing looks like a phone book, no wonder every girl in this city is walking funny."

little brown book by mitchy P February 13, 2014