My birthday is in the middle of winter, so what people should do, is to go out and build snowmen in the streets stopping all traffic everywhere. Afterwards there would be free hot chocolate and waffles for everyone.
I dunno, fireworks & tongue-in-cheek oratory sound good to me.
Guinness, Mexican food, dark chocolate, and old movies for everyone!
well, my birthday is in the spring, so there would be pretty (not itchy!) dresses for all the girls, flowers, and dancing.
People would eat gazpacho and guacamole and things like strawberries and raspberries and salads with berries
there would be horses. Maybe a parade with horses.
Wine and stuff for the adults, I guess. I don’t really know.
People would celebrate with ribbon dancers. like the ones rhythmic gymnasts use.
The whiole atmosphere would be… picnic-y. Easter is usually still too cold to spend the whole day outside, but April 28 isn’t so bad. People would have picnics, ride horses, maybe go hiking or go skip rocks or feed fish… that kind of thing.
Oh, and presents and candy too. Not big ones like christmas where everyone goes broke. But like St. Nicholas Day size.
My birthday is already a holiday. Not just a national one, but a nearly global one. I believe most people probably spend it nursing a hangover.
ETA: my 21st birthday was particularly sweet. The whole world was celebrating that one. Rolling news coverage and all. 
May 15th.
I want an outdoorsy BBQ and fireworks day like 4th of July combined with flamboyance and debauchery of Mardi Gras or St. Patrick’s Day. Some type of effigy or ritual like on Guy Fawkes Night would be a bonus.
My birthday is a public holiday sometimes (if it falls on a Monday). It’s the Queen’s Birthday, which is a total scam as not even the British have such a thing. It’s just a day off work. As a small kid, I remember my dad told me people were letting off fireworks because it was my birthday.
But if it were to be a holiday for me, I’d want it to continue the true Australian tradition: everybody would think of it as a day off work. People would get drunk and play beach cricket. Nobody would give the origin of the holiday a passing thought. If that happens, I’d have succeeded. I’d hate for it to be meaningful or anything - just go out and drink beer.
If it’s good enough for the Queen, it’s good enough for me.
Everybody eats unlimited pizza, fried chicken, cheesecake, coconut cream pie and anything containing peanut butter.
Oral sex, all day.
Listen to Rachmaninoff.
Adopt a cat.
Only same-sex couples can get married.
Sounds like the perfect day.
I think they are nursing their hangovers from the celebration of my birthday.
Susan
(Daddy’s Little Tax Deduction)
Everybody give everybody Reese’s Peanut Butter Cups. (Including me of course.)
Everybody wear a hat.
Everybody sing in the street like they’re hopelessly deranged.
And everybody adopt a kitty, because a jillion kitties need homes.
Free Manolo Blahniks all around! 
VCNJ~
Just remember, you will be dead. They don’t give you a holiday until after you die.
On my birthday holiday, people will probably tend to leave the country. 
Go to the library, walk the stacks at random, find a book on a subject you’re ignorant of that looks interesting and accessible to you, and give it a try.
This also has the benefit of being a way to hook up with people. Books are natural aids to breaking the ice – and we all come off as a tad smarter with one in hand!
Probably stand quietly for the next several hours while the names are read off of the memorial…
Every available woman must seek out and kiss an available engineer. No hanky-panky, merely lippus-lockus.
The duration and intensity of said kiss must be proportional to the engineer’s lack of personal hygiene.
Directly or inversely?
It will be good that the banks and schools will be closed—this will give everyone extra time to prepare for the traditional masqed balls that will be made open to the public in every major city although private persons are free to celebrate with costume parties, too.
There will be cake.