How is King's blood deemed?
Stark blood is King's blood because they were Kings of the north thousands of years ago?
Baratheon blood is still Kings blood because Robert sat on the throne for a couple decades (but there is no [blood] Baratheon monarch anymore)?
Targaryen blood is Kings blood, even though there are none on a throne until Jon's recent appointment as King of the North?
Mance Rayder and his son's have King's blood because he was called the King beyond the Wall?
Is Greyjoy blood King's blood, since they claim to have a King of the Iron Islands?
Where does it end? Did Xaro Xhoan Daxos have Kings blood after declaring himself the King of Qarth? How many different bloodlines does King's blood run through?
That'll put marzipan in your pie plate, bingo!