When the clock rolls over to 12:00 AM on January 1st, 2000, six billion voices in a billion different languages will shout out a single phrase with a single, unified mind... "HAPPY NEW MILLENIUM!!!"
About 2 seconds later, the pundits will start screaming how it's not the next millenium for another year, and seeing as they'll all be too drunk to think straight this will lead to a fist fight. By the time the brawl dies down and they realize that the world hasn't ended and the Y2K bug hasn't so much as shut off a single lightbulb, it will have become the year 2000 in the next timezone over where they're still expecting the apocalypse despite the fact that for half the world midnight 2000 has come and gone, and the whole fiasco will start all over again...