Avast ye! I have not knitted a pirate flag, though I have several piratical projects in my queue.
This pirate hat and its matching set of pirate mittens are a must-have for any well-dressed pirate There are Jack Sparrow’s Favorite Socks in the “Black Purl” colorway and the Buccaneer’s Booty socks as well.
And while this Pocket Pirate is crocheted rather than knitted, she’s too adorable to leave off the list.
But a flag? It could be done, I suppose. I might end up wanting to use it as a blanket instead. The salty water of the high seas wouldn’t do good things to the wool, anyway. Hmm… a pirate blanket…
Edited to add: there is a comprehensive list of pirate-themed patterns here.