Shacknasty is a corruption of a Modoc Indian name meaning Left-handed.
I'm shacknasty and have worked with an inordinate number of shacknasty surveyors through my career. Seems like the general population is about 10% shacknasty and from my experience the percentage of shacknasties in the surveyor population is greater.
This term was brought to my attention researching the Modoc chief Captain Jack (Kintpuash) and his 1873 battles against the US Army in southern Oregon/northern California called the Modoc War. Long story short, after besting the US Army, the Modocs got away. Some of the former Modoc leaders (Hooker Jim, Bogus Charlie, Steamboat Frank and... drumroll... Shacknasty Jim) turned themselves in and then hunted down Jack for the USA. Jack was hanged at Fort Klamath Oregon along with 3 other warriors.
So us south-paws have the following words associated with our handedness:
Gauche. French. It means tactless or crude, but in the original French is means "left"
Sinister. Latin. Evil, the Latin word for left
Shacknasty. Corruption of Modoc word for left handed. Apparently Shacknasty Jim had two brothers, Jake and Shacknasty Frank. Guess which brother was a lefty.