Bak is an internet accronmym for straight back at keyboard. Acronym for a Bad Ass Child. It isn't meant in a confident way, it indicates the child is nasty, disrespectful, backtalking, disobedient, spoiled, etc. etc. Slang for 'back'. Lazy individuals make use of this a great deal to signal people they know once they say BRB or BBL. their state of going african on someone.