Very Bad Word

A student called me one of the worst words in Korean today, and I didn't even know it. It's funny when people say mean things about you in a foreign language, because, well, you don't really know how to react (I shouldn't generalize... I didn't know how to react.).

The student was angry with me for taking his spelling test (again with the darn spelling tests!), but I only collected it after he stopped halfway through, claiming it was too difficult, and then began looking up the answers while I was still giving the test to the rest of the class. I heard him loudly mumble something about sheep, except that wasn't what he said. Then he stormed out of the room. The other students (all girls) looked utterly shocked, but because I'm accustomed to this particular boy's outbursts and tantrums, I ignored it until finally, the girls could no longer contain themselves. Very solemnly they told me he'd said something very, very terrible. They wouldn't repeat the word but kept saying how bad it was. Finally, one of them agreed to write it down on a piece of paper which she did using the faintest of pencil strokes. I then took the paper to the Korean teachers who all audibly gasped when I showed it to them. They looked horrified, and even they wouldn't tell me what it meant. The event culminated in the boy getting a strict reprimand from one of them. 

Meanwhile, back in la-la foreigner land, I still have no idea what the word means, only that it's completely awful, so I won't be adding it to my current rotation of six Korean words.