I called it "Cheonji Day" instead of Teacher's Day because Teacher's Day is also known as one of the most common days for parents to give teachers cash gifts called "Cheonji" (촌지))... sometimes meant to be in exchange for "special" treatment of their kid (on the grade sheet) -- there have actually been laws passed putting a maximum on the amount of cash or value of gifts permitted to give teachers, because the old tradition of bribing the teacher had gotten so rampant. The practice continues today.
My favorite Teacher's Day moments in Korea came from my first year, when I taught grade school kids.
Being male, the usual cosmetics packages didn't suit, and there must have been a sock-selling truck somewhere on the bus route picking kids up to come, so over the course of the day, I received twelve pairs of the exact same socks. Totally interchangeable. I didn't buy socks once my first three years in Korea. Just when I was starting to run out and wear out, another teacher's day would come along. It was awesome.
My favorite teacher's day class was the class where one student gave me a bucket of rock candy, and another student gave me a bottle of Amway toothpaste. Perfect match.
My biggest teacher's day bung-up was the year I told the students that if they wanted to bring me Teacher's Day gifts, they could, but please remember that I'm allergic to milk, so chocolate presents make me sad, because I can't eat Korean chocolates (it's all super milky), and the mothers took my PSA to mean that I was expecting nice gifts from all of them, and complained about my overly expectant attitude. Since then, I've just taken the chocolates humbly, thanked people kindly, and passed the chocolates around to the other teachers in the staff room (who are all swimming in chocolate, too).
Thanks for the spelling correction, ROK Hound.