Being "Bitch Tagged" means when a "friend" puts a photo up on facebook of you and tags you as "Bitch" The tagger can also use other words such as "Faggot, Loser, newb tuber." Whatever they feel is commical.
Bob: Hey, saw that picture of you on facebook, bitch.
Pippin: What?
Bob: LOL, you were "Bitch Tagged." on facebook.