Generally a derogatory term for black person. It comes from the combination of "chou" (as in chounikwa, Laquichou, or chouquelle) and the japanese name "Mika", so is a slur for someone having negatively-viewed stereotypical manners of an African American and the prudence of a Japanese teen.
"She can be a douche sometimes. 22 and she hasn't even been laid. Such a choumika"