Mad Hatter's 'unbirthday' party

The Mad Hatter seems to enjoy any excuse for a party! He and the March hare wish Alice a Happy and Merry 'unbirthday' 

Obviously confused at such nonsense she initially disregards their intention.

What has occurred to me is that everyday (364 days a year) is an opportunity to wish someone all the best and tell them all the wonderful things that you love about them, that too often are saved for the birthday card spiel.