South Korea didn't have a very good time at the World Cup, finishing dead last in their group after losing to Algeria, losing to Belgium with only 10 men, and tying to Russia. It was their first World Cup without a win since 1998.
They also didn't have a very good time returning from the World Cup, as fans showed up at Incheon Airport to throw toffee at them. (Yes, toffee.)
You're probably a bit confused, which is understandable, but Sky News offers the information that "go eat toffee" is an insult in South Korea. Personally, I don't think anything that winds up with me getting candy is bad, so the South Korean team should keep their chins up.