What is Hangover Day?
1.
AKA New Years Day (not to be confused with New Year's Eve)
It is called Hangover Day because..
well it's obvious
everyone has a hangover today because of excessive drinking at New Year's Eve parties.
Sober Person: Hey Lofonduh, wanna go to the mall today?
Lofonduh: Naww.. my head hurts too much.
Sober Person: But no one will come!
Lofonduh: That's because it's Hangover Day.
See
2.
The day after New Years. You had a little to much to drink that last day of the year and now for the first dayof the new year you can celebrate with all the other hungover people, or you could sleep.
Person 1: Dude my head kills from last night.
Person 2: Another typical hangover Day.
See