So my rowdiest middle-school class were talking about their Korean teacher in class today. I have shared quite a few classes with their teacher over my time here, and I know her to be kind and popular with the students. Still, I wasn't surprised these guys were saying that she is very strict and always hits them. And that (of course!) they are perfect students who never do anything bad to cause this. Then the instigator of the conversation leaned back, put his hands behind his head, and said '변태' (byeon tae), or in English, pervert. He was rather taken aback that I understood the word, and someone else started explaining that the teacher was always touching them for no reason. It was very obvious that they were joking, but my Western sensibilities panicked. This would be serious stuff back home!
So in the break between classes, I asked our Korean manager what I should do. She chuckled, and said I should just let the teacher know, and she could deal with them. So, right before the next class, I did. When some of the other students realised what was happening, the boy in question ran into the hall and threw himself on the floor in a hugely entertaining display of humility.
It seems that in Korean, calling your teacher a pervert is just part of the usual banter. Glad to have that one cleared up.