Like the very similar term hosehead, the term may have referred to farmers of the Canadian prairies, who would siphon gas from farming vehicles with a hose during the Great Depression of the 1930s. The expression has since been converted to the verb 'to hose' as in to trick, deceive, or steal - for example: "That card-shark sure hosed me." Hosed has an additional meaning of becoming drunk - for example: "Let's go out and get hosed."
The term "hoser" also refers to an era in hockey before the ice resurfacing machine came into use. The losing team had to hose off the ice. The term "hoser" can then be construed to mean loser.
Another possibility is that it might be related to the term hoosier.
Today, the word hoser evokes - sometimes sympathetically, with gentle ribbing, and sometimes negatively - a stereotypical Canadian male, typically lower to middle class, white and English Canadian. He is especially concerned with drinking beer and watching hockey or curling. The hoser is understood as a product of a poor and white upbringing, but never from a more cosmopolitan lifestyle — he is more likely to come from a small town or a rural farm community than a big city, although hosers may also exist in the suburbs of major cities. He is generally assumed to be unemployed, although he may also be a farmer, a labourer working in primary industry (manufacturing, mining, forestry, etc.), a tradesman or a manual labourer. He is typically not university-educated: if he has any education past high school, it's a college trade program. If he does go on to university, or moves to a city, he will still have preferences for "hoser" food, clothing, music, and sports, and will retain the language inflections of his upbringing.
He's often imagined wearing heavy winter clothing, usually a flannel lumberjack shirt, Kodiak boots and a tuque. He is generally a young adult to middle age, and may be somewhat aggressive given the beer and hockey, but may conversely be passive and amiable, given the beer. In musical culture, he is correlated with classic and mainstream rock music, particularly with Rush, April Wine, Trooper, Nickelback and the earlier, rowdier works of The Tragically Hip. If he goes out socially, it's usually to a doughnut shop.
A hoser's flannel shirt may also be referred to as a "Kenora dinner jacket". (Some regional variations of this term also exist, usually substituting a hoser-stereotyped local community's name in place of Kenora.)
A woman who dresses and acts similarly may also be referred to as a hoser, although this is much more rare.
Hoser may also refer more generically to a rude and unkempt person, similar to the more universal terms boor, slob, and lout. However, like other such terms (e.g. jerk) it can also be used in a much more general sense as an all-purpose mild insult. The term is also sometimes used outside of Canada as a mocking term for any Canadian, although this usage may be perceived as offensive because of the word's more particular meaning within Canada. (See Anti-Canadianism)
Bob & Doug McKenzie defined the term as "What you call your little brother when your mother is in the room."
Perhaps the iconic representations of this definition of hoser in Canadian culture are Bob & Doug McKenzie of SCTV and Strange Brew. This model also profoundly informs The Red Green Show, Trailer Park Boys, Kevin Spencer, FUBAR: The Movie, Chilly Beach, and some sketch characters on Royal Canadian Air Farce (e.g. "Mike, from Canmore", "A Canadian Moment"), and This Hour Has 22 Minutes (e.g. Connie Bloor, the Quinlan Quints).
Its use was also popularised in poker circles by Bill Chen, who was once, in jest, famously described by David Sklansky as "the World's Biggest Hoser". The word has become commonly used in poker ever since to describe any "fish" or bad player who is a long-term loser at the game of poker.
This term is also recognized as being used to describe something that interferes with or “messes up” something else.