An ex-boyfriend of Mexican ethnicity, specifically an immigrant from the country of Mexico. A shortening of "Mexican ex-boyfriend." Used by whites in a self-deprecating way, as in a girl who has a Latin fetish, for example, and usually not meant in a derogatory or anti-Mexican manner. See also Nexican
Susie: "I've got to find a new boyfriend. Things have been dry around here since the Exican and I broke up."
Jennie: "I know a good-looking bartender. He's a good potential Nexican for you, Susie."