Well, I thought that Boston's always been kind of a testing area for new lingo, so it wouldn't be that weird for "douchebag" to take hold there before spreading out to the rest of the country. In fact, it'd be downright wicked.

For me, I heard "douchebag" on that Saturday Night Live sketch with Lord & Lady Douchebag, but then didn't hear it much at all until around the mid 2000's. Maybe it was a regional thing?