From a quick search on google groups, I found this:
"Originally meant someone who messes up someone else's plans or work.
Now it usually means an inarticulate, beer-drinking lout.
It comes from the earlier slang verb "to hose" meaning to defeat soundly as
in "we hosed the opposing team" but it now usually means to mess-up though
sometimes it means to deceive, swindle or outwit.
Presumably the verb came from 'to hose down with water but there may be
other explanations."
Edit - another post said this "My college roommate, a canadian import, described the origin as
referring to a certain feminine hygiene device. "