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.
***********************
In the meantime,
Bo Diddley cranks out the notes on his guitar.
Then he says:
Bo, you don't know
diddley!