A slow-witted and incompetent person
A). Nigger
B). Snotty
C). Snotty
D). Duffer
Duffer
One word substitute is Duffer.
Nigger: a contemptuous term for a black or dark-skinned person.
Dud: a thing that fails to work properly or is otherwise unsatisfactory or worthless.
Snotty: full of or covered with nasal mucus.
Duffer: an incompetent or stupid person.