n. — proprietary, Saskatchewan, Food & Drink
chocolate milk (see Image 1).
Type: 1. Origin — The term was originally an abbreviation for "vitamin concentrate" (see the 2008 quotation), and later became generalized in Saskatchewan to mean all chocolate milk. Vi-Co was trademarked in 1933 and again in 1957 by Chocolate Products Limited, a company based in Ontario (see Canadian Trade-marks Database references). The Saskatchewan connection is profound (see, e.g., the 2007 quotation) and is likely a preservation and generalization of this early 20th-century trade name (much like "Kleenex" for paper tissue, for instance). The term is most prevalent in Canada (see Chart 1), of which almost all uses come from Saskatchewan, although our regional internet resources did not allow for the creation of a chart.
See also COD-2, s.v. "Vi-Co", which is marked "Cdn (Sask.) proprietary".
- 2000  Saskatchewan has no yuppies. The yuppie existence is, by definition, and for lack of a metropolis, demographically impossible in this province. You know how Alberta is forever boasting that it is rat-free? Same deal. Except that if Alberta ever wants to talk trade: no way. It is not that young people, or urban folks, or professionals, are unwanted individually, or that city dwellers with white-collar jobs who are not old are less than welcome. The only undesirables are the shallow, materialistic, pretentious rich snots: "yuppies," as the description is used colloquially, with the stigma attachment.
- You drink the diet meal-replacement formula, like a yuppie. The only way you can choke it down, though, is to think: Vi-Co, Vi-Co, Vi-Co. 
- 2007  "I always refer to chocolate milk as Vico," says Kristy Pryma, a Saskatoon expat and creative director at High Road Communications in Toronto. "It's less brown than a pinky salmon colour, especially if it comes out of a fountain dispenser. I think there's a certain amount of retraining required when you move here. When I ask for Vico I just get a blank look. Same as when I ask for a bunnyhug." 
- 2008  When the Saskatchewan Co-operative Creamery Association first introduced chocolate milk, two imported flavouring syrups were tested, by far the most popular of which was called "Vi-Co," short for "vitamin concentrate." The working title stuck as a retail brand name, eventually to become synonymous in Saskatchewan with chocolate milk, even now, despite the discontinuation of the label in 1995. 
- 2011  Still on the topic of trademarks, apparently there's a practical reason for the persistence in Saskatchewan of Vi-Co. A diner is just as likely to baffle a waitress with an order for chocolate melk. I was wholly unaware that for my entire lifetime I've mispronounced milk as melk, as do my children, apparently, until a contributor to one of many Facebook pages proudly dedicated to all things Saskatchewan mentioned that she is constantly corrected by friends in Calgary (us: Cal-gar-ee; them: Calgree). Like Eyetalian spaghetti, served in Moose Jaw, Estevan and Yorkton and heavy on the long vowel I, as opposed to Italian spaghetti, a popular dish in Venice, melk defies explanation. 
- 2015  Youth especially are known for creating slang as social markers, and use of particular words can help identify a person with a certain generation, given that most slang has a lifespan of 25 to 30 years, Makarova added.
"Vi-Co" turned into slang for chocolate milk as a generation of Saskatchewan residents chugged Vi-Co brand chocolate milk from the now-defunct Dairy Producers company. The Insightrix survey found this particular slang is most recognized among residents age 35 and older. 
Images:
Image 1: A litre of Vi-Co. Source: http://laiteriesduquebec.com/divers/divers.htm. Photo: D. Morin
Chart 1: Internet Domain Search, 16 Oct. 2012