천만에요 is a well-known Korean expression which almost always appear on Korean language textbooks. But that expression is rarely used in real life. (To be more precise, I think the frequency of that expression being used is very different in textbooks and real life.)
I tried to think about more such examples, but I couldn't think of any. What are such Korean vocabularies, namely often-used-in-textbooks-but-not-that-much-in-real-life?