I was going to say New Year’s Eve, but it turns out it’s also Make Up Your Mind Day. (And Unlucky Day, but that’s obviously bullshit.)
Pistol Patent Day.
Huh. 
D-Day.
U-S-A! U-S-A!
According to this, mine is National Dessert Day. More to the point, though, it frequently falls on or near Thanksgiving (ours).
It just seems like such a heavy food for hot weather. I would prefer a nice cold pasta salad or something. (Followed up by cake, naturally.)
Evaluate Your Life Day?!?!!??
Really!?
Holy Experiment Day and Hug a GI Day.
I love it.
1 May Day
1 Loyalty Day
1 Mother Goose Day
1 Save the Rhino Day
Festivus? Seriously? Two days before Christmas, already ripped off (as a child, of course) in the celebratory arena, and all I get is a Seinfeld holiday? Oh, and “Roots day”, which I’m pretty sure they just made up.
Usually I call it TimeWinder’s Birthday National Holiday, and society must agree, since they almost always give people a day off from work/school to observe it.
United Nations Day.
I was born on the very day the United Nations’ permanent NYC headquarters was dedicated.
The tapioca pudding must be stopped!
And I was born on the 33rd anniversary of the UN’s first General Assembly, in London. Also the 59th anniversary of the League of Nations’ first meeting, when the Treaty of Versailles was ratified.
Cooool… we must be related. 
Caramel Popcorn Day!
Woot!
And Easter, occasionally.
Mine is “Read Great Poetry Day” and “Kiss Your Mate Day” and that means I’ve got less than two weeks to pick a poem and find a mate. Pressure. Great.
Dentist’s day…off to floss.
National Bird Day
::sings:: Happy bird day to me, happy bird day to me…
I never thought there was a holiday on my birthday.
It turns out there is: Teddy Bear Picnic Day.
On second thought, I was right.
Heh. Also known as the day when “nearly every possible sort of bad shit that could happen has happened day”
Kennedy Car Accident, Planes falling out of the sky, Earthquakes, Civil Wars started, Vin Diesel’s birth, and all sorts of good stuff. I don’t think a boat has sank on our day though.
National Freedom Day, bitches.
Also, Super Bowl Sunday, occasionally.