This is a catch phrase that originated in a TV ad in the late Eighties that featured super athlete extraordinaire Bo Jackson and rock'n'roll pioneer Bo Diddley (he's notorious for his famous box-shaped electric guitar). Basically, the term means that somebody doesn't know doodly squat.
The narrator says:
Bo knows football.
Bo knows baseball.
Bo knows weightlifting.
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In the meantime, Bo Diddley cranks out the notes on his guitar.
Then he says:
Bo, you don't know diddley!
This is for Rachel you big fat white nasty smelling fat bitch why you took me off the motherfucking schedule with your trifflin dirty whiteracist ass you big fat oompa loompa ass bitch i’m coming up there and i’m going to beat the fuck out of you bitch
Karen: Where is your manager?
Manager: T.I.F.R.Y.B.F.W.N.S.F.B.W.Y.T.M.O.T.M.F.S.W.Y.T.D.W.R.A.B.F.B.O.L.B.A.I.C.U.T.A.I.G.B.T.F.O.Y.B