'Douche' and 'douchebag' were in high rotation in my Cleveland-area elementary school in the early-mid 90s. At the time, it didn't have the smarmy connotations it has now, probably because the kids using it were most likely smarmy, self-assured douchebags themselves.

As a kid, I just kind of assumed it (along with all the other mysterious puzzling-at-the-time vulgar words the stupid mean kids used, like 'fag', etc.) must have come from Beavis & Butthead. But in retrospect that word probably wouldn't have been allowed on cable TV at the time. Who knows how it got around.