A less recognized, but more acute diagnosis of a "vanillaface" affected by some personality disorder suggesting, but not limited to, the participation in activities prominently attributed to African-Americans and/or the belief that he/she has African heritage and is black. This is a term describing mental illness and is not to be confused with the derogatory term "wigger".
SON: Yo ma, i gots sum to tell ya'll.
MOTHER: Yes, sweetie?
SON: The doc says my nigga self is niller.
MOTHER: Oh my God! Is it contagious?
I hate those damn nillers.