A very special day

When you were a small child the most important dates on your calendar were

• your own birthday (you would get presents, grandma and grandpa would visit, you could invite all your best friends to come over, etc.)
  
• christmas (same reasons, except everyone would come over without you needing to bother with invitations)
• new years (any day where can stay up late, is cool)
  

Now you're older every date seems like an important day. If you're married, you better remember your spouse's birthday and your wedding day. You've got a day for the animals, the fathers, the mothers, gay pride, pink ribbon day, aids awareness, Independence Day, Superbowl Sunday, Liberation Day, 9-11, 7-7, march1, etc.

And you're in even more trouble if your favorite date happens to be for example your birthday, and then something like an assassination on a politician occurs on the same day.

You here's a question: how bad does some event have to be, before it overshadows an otherwise good day?

Worse yet, how climactic does it have to get before we have to invent a completely new calendar?