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!
A phrase popular in the LGBTQIA+ community to refer to trans men or transmasculine nonbinary individuals who adopt a more confident and exuberant demeanor once they start transitioning.
Sometimes t-boy swag is used in a light hearted, tongue in cheek way to describe a stage where trans masculine folks are new to presenting masculine and still finding their style.