Bob the uncle who raped u as a young child. Everybody knows, except 4 u. U were knocked out by bob when he was raping you. So u dont remember. Changed his name too. We all laugh behind ur back.
I'ts been a while since I heard of people using this phrase. I remembered reading the phrase from a game magazine giving tips and all and nearly at the end of the tutorial comes up 'and Bob's your uncle'. I was kinda random for me but I find it pretty funny.