Well, my nickname was given to me by my wife. She called me her big bear because of my bearhugs she used to love. I also enjoy astronomy and I thought that ursa major would match my nickname but it sounded too feminine, so I changed it to OsoMajor.
BTW, NO&DO...I really like your nickname. Regarding the use of the word Yankee to refer to Americans even Southerners. Yes, it's a reference to all Americans from outsiders, but as a native Texan, I can tell you right now that no Texan would ever call himself a Yankee!