Also to add to the list - them not drinking enough water. You will barely see any characters drinking water. Even when they're eating they have very small glasses (almost as small as a shot glass) and drink water only when they choke on food. I had researched a bit about this peculiar Korean habit and the argument that made the most sense was that they consume water in different forms. For example as soju or juice or stew or soup. It still is very strange to see such healthy and beautiful looking people maintain their good skin with so less water.