Dec. 31, 1990. I celebrated by staying home and defrosting the freezer.
In general, New Year's Eve sucks. It is, I maintain, the most overrated holiday of the year.
If you're curious, the most underrated holiday is St. Swithin's Day, mostly because 1) it's fun to say (really--try saying "Me? I'll be celebrating St. Swithin's Day in Southampton--how about you?" out loud), and 2) it sounds made up. (A close runner-up would be Setsubun, in Japan. Any holiday that involves hurling beans indoors is all right in my book.)