My dad and I agreed on having an "end of the world party" over 5 years ago. He just so happens to be flying in the morning of the 21st. I wonder if he remembers.
5 years ago my friend (who nowadays is really beautiful, has guys falling at her feet) said she would invite me to her 18th birthday party. We stopped talking for nearly 4 years but she still invited me :3 (sadly I couldn't make it). But this is your family. I'm 120% sure he will remember.
