Can anyone explain back slang to me?

I have some friends that constantly speak in back slang.

But we all come from west Sussex and none them have strong northern routes (we are all 'posh girls').

I would like in an ideal world to be able to speak it but i suck at languages. Can anyone teach me how to speak or learn what it means...?
Update: im not a posh girl and i do mean BACK slang not BLACK!!!!!
Update 2: im not a posh girl and i do mean BACK slang not BLACK!!!!!
Update 3: i cna look after my self thanx i wont get beathen up!!
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