Answer:
I'm not sure if you mean stereotypes in kdramas that are not entirely true or something but here are some that I know.
-School life: School life in south korea is not as glorious as shown in dramas. It is super super stressful. Students often spend 12 to 16 hours in school, including academies. In fact, students started consuming way too much caffeine that they recently introduced a new law that stops students from drinking too much caffeine.
-Rich handsome young CEOs: Let's be honest, most CEOs are middle aged men or just normal business men like in all other countries. Most people believe and fantasize that real life is like in the kdramas.
-Everyone is good looking: Most locals are just average looking people like you and me. Not everyone has actor worthy visuals. (Of course I'm not saying that they are ugly. Everyone is beautiful in their own way.)