What is the unluckiest birthday ever?

Answer 1

A birthday may be "unlucky" when it coincides with a holiday -- when there are other things to be celebrated, other places to go, other presents or gifts to receive.

December 25 - Christmas

December 31/January 1 - New Year's celebrations

February 14 - Valentine's Day may distract others, or help friends remember

Late November - Thanksgiving (fortunately this is not a fixed day); travel by family members may result in lower or possibly higher attendance on some birthdays celebrations. The same can occur for individuals who have nearly the same birthday as other family members. But this can be any date.

Also

If a birthday coincides with some unpleasant historical event: September 11 or in previous generations December 7 (Pearl Harbor).

February 29 is another problematic birthday, but it can also be seen as special.

Answer 2

13