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1.
It means to fuck some ones mother backwards. almost as if you where to fuck them the wrong way. commonly used as an insult to tell some one

1- to fuck there mother

2- in a way that would be back to front and all wrong

3- to insult someones intelligence and mother.
jack mason: Rob you eat balls
Rob Harvey: Go fuck your mother backwards
by robertH1230123 February 12, 2010