This noun in commonly heard in the northern New York area, bordering Canada and Vermont. It is used to discribe a person that is like "trailer trash," but with hick tendencies to fit the north country personna.
That guy with no teeth is a cheewee.
A person that exhibits a disgusting appearance. Typically a female. They may be missing teeth and use the little money they have to buy lottery tickets. Sometimes they exhibit "Skanky" actions. They are normally older in age as well, and their clothes may be deteriorating "hag." So when you put those two words together, you get scag.
That lady is such a scag!