It doesn't seem so obscure after two people have made it in nearly identical lingo.

That said, I have no idea what it references.

The "Dread Pirate Roberts" moniker is from a (wonderful) movie called "The Princess Bride". In it, the hero assumes the mantle of the "Dread Pirate Roberts", and is at least the fourth successor to the title. It's an interesting factor in this case, because the choice of name hints that the "Dread Pirate Roberts" handle was chosen so it could be passed from person to person.

https://www.youtube.com/watch?v=aHZGqBVBCRw

Notably also the judge has apparently admonished the jury not to watch The Princess Bride:

https://twitter.com/sarahjeong/status/555847465128435712

Inconceivable.