The Korean couple calendar: 100 days, Pepero Day, Black Day

Korean couples count the days since they started dating. The 100th is the first real milestone, then 200, 300 and 1,000. Some couples start counting at 22.
The 14th of every month has a name attached. On 14 February, Valentine's Day, women give to men. On 14 March, White Day, men give to women. The order is the reverse of what most visitors expect.
14 April is Black Day. People who received nothing in February or March eat jajangmyeon, noodles in black bean sauce, on that day.
11 November is Pepero Day, named after a stick biscuit that looks like the number 1. Convenience store counters disappear under boxes of them.
Christmas in Korea is closer to a couples' night out than a family day.
For a traveller this calendar is also booking information. Restaurants and date courses in Seoul are busy on these dates. If your concert falls on one of them, reserve dinner before you fly.