Wikipedia
Chilango is a Mexican slang demonym for residents of Mexico City. The Royal Spanish Academy and the Mexican Academy of Language give the definition of the word as referring to something "belonging to Mexico City", in particular referring to people native to the capital.
The term Chilango is widely used and refers to a variety of people, ranging from those who speak with a Chilango accent, to those who live, work or study in Mexico City. Some people claim that people who are born and raised in Mexico city are called "Capitalinos or Defeños". However, most Mexicans of the 31 Mexican states do not distinguish between native Mexico City inhabitants and those who moved there, and call all residents of Mexico City "Chilangos", or even "Chilanguillos," an even more pejorative term.
Two other terms used for a resident of Mexico City are Defeño (derived from D.F., Distrito Federal and not an official Spanish word) and Capitalino, which are also sometimes used both in a positive or a derogatory sense, although the latter is generally accepted as a neutral demonym. The terminology can also be used for a person born in the suburbs or surrounding areas of Mexico City who has moved to Mexico City. Sometimes it has a negative connotation when used principally by someone in one of the 31 States of Mexico.
"Chilango pride" has also led the term "Chilangolandia" in reference to Mexico City. They also consider that any non-Chilango who uses the term does it in a derogatory fashion, and although widely used, it is considered pejorative since it is not uncommon for people not from Mexico City to view Mexico City dwellers as "different" from them. The embracing of this term also led to the publication of Chilango, a monthly humorous magazine, in November 2003 in which real events conform the majority of articles but trying to make fun of the city itself. It included within its pages the Time Out city guide, but this was retired in early 2007. Chilango was described in the December 2004 version as:
There are many theories on the origin of the word "chilango". One of them is that it derives from the Nahuatl word Ixachitlān, that actually refers to the whole of the American continent. The word "shilango" has also been documented to have been used in the Veracruz area to mean people from central Mexico, and coming from the Maya "xilaan" meaning curly or frizzy haired. Yet another theory is that it comes from the Nahuatl "chilan-co", meaning where the red ones are, and referring to the skin, reddened by the cold, and used to refer to Aztecs by the Nahua people in the Gulf of Mexico There is a popular phrase used by people outside Mexico City that says: "Haz patria, mata a un chilango" that means Be patriotic, kill a chilango. It's not intended to be used literally but with a mocking tone instead. The phrase, coined in the state of Sinaloa, reflects an attitude common in the northern states of disdain and rivalry against residents of Mexico City, that peaked in the 1980s. Then, as a response to this used phrase, Chilangos themselves began to add "Haz patria, educa a un provinciano", which means, Be patriotic, educate a rural person. People in Mexico City refer to "provinciano(a)" a person from a rural area who does not live in a major city or town.