New Zealand's Boxing Day
As an American, when I first heard of my New Zealand friends referring to Boxing Day, I thought it was a day of watching sports on TV the day after Christmas. Turns out, it's much cooler than that lol.
As @NatDudley explained to me, it is a National Holiday for Leftovers. Seriously! You take your Christmas leftovers and bring them to your friends house, where you have a delicious meal and hang out. That is exactly what I did today!