At Game 7 of the 2006 ECF in Raleigh (I was lucky enough to be there), the fan giveaway was a Hurricanes nice beer glass, but instead of a plastic one like in most cities, it was actual glass. Fueled by the heart-wrenching loss and a tailgate party that had been going since 1 in the afternoon, a not-super-tiny number of drunken buffalo fans proceeded to smash the glasses on the ground outside the arena after the game. Several were arrested. It's not like more than a couple dozen bozos were doing it, but that's enough to create a stereotype. That series had seen a lot of AM-radio-fueled cousin-marrying and armpit-of-the-USA jokes too, so tensions were already pretty high.
The myth has grown over the years to include things like abducting women and eating babies, but suffice it to say the Canes fans don't much care for the buffalo transplants who take over their arena twice a year.