Bob and Doug Mackenzie from SCTV are believed to have coined the phrase.
lts to refer to someone who has done something stupid or has a history of stupidity. Or sometimes used to refer to other Canadians.
example 2-HAHA I FEEL LIKE SUCH A HOSER SITTIN HERE WATCHIN' REDGREEN SHOW DRINKIN TIM HORTONS IN MY LEAFS JERSEY...
example 3- FLY OFF, YUH HOSER! piss off..fuck off..get lost..you loser/poser/idiot/jackass..
example 4-AW C'MERE YA BIG HOSER AND GIMME A HUG said drunkenly with a keg of molson in hand
Come here hoser, I was just kidding.
Used as a negative, it basically means "idiot." When used positively, it's a phrase of light endearment.
In both cases, it is most effective when the subject(s) displays stereotypically Canadian attributes.
POS - "They drank all our beers and smoked all our smokes, but took the ski-doos to get more before the hockey game started. What a bunch of Hosers."