Shouldnt it be 'happy birthday - anniversary'?

Because birthdays are healthy.  The more a person has, the longer they live!
 
Duh. 
 
(On the flip side, birthdays beat the alternative!)

Yes, it's only an annual observance of ones expulsion from the maternal fecundatory oven, but the word "birthday" sounds better.
 

Well I didnt mean to challenge the celebration itself, just the nomenclature.
 
Or why not call it 'another year closer to death - day'?
 
Im macabre. 

Or, go read Alice in Wonderland and see what the Mad Hatter's Tea Party was celebrating.

craigb
Or, go read Alice in Wonderland and see what the Mad Hatter's Tea Party was celebrating.

Wasnt he just stuck in time thus constantly having a tea party?

No, see post #5 above.

craigb
No, see post #5 above.

Im confused.
 
'The Hatter explains to Alice that he and the March Hare are trapped in a never-ending tea party because, when he tried to sing for the Queen of Hearts at a celebration, she sentenced him to death for "murdering the time." He escaped this fate, but Time, out of anger at his attempted to "murder", has halted himself for the Hatter, keeping him and the March Hare at 6:00 pm forever'.

The real question (that applies) is "What do they celebrate?"

craigb
The real question (that applies) is "What do they celebrate?"

Oh I just found the lyrics to the song.
 
They are celebrating one of the 364 days of the year that are unbirthdays.
 
The hell why am I actually researching this?