Cursing at my Class

This week one of my text books, which heavily emphasizes vocabulary and listening, had two very similar words: canyon and canon.
I noticed in my first class that the students kind of giggled when I was explaining the difference between these two words. But that's somewhat common, so I didn't think much of it.
In my second class, for some reason, I really emphasized the difference, and I said "CAN-YON" again and again with very deliberate pronunciation. Before I knew it, the whole class was saying "canyon" and giggling to their neighbors. Some were just laughing outright. I realized that I must have said something funny. I asked what they were laughing about, but nobody was willing or able to tell me. Finally, one of the students said that it was an easy word to pronounce and that I didn't have to keep going over it. I just thought I had drifted off into teacher LA-LA Land, where I was droning on and on about something not so important. (This is actually easy to do since I teach the same exact class 5 times.)
In my third class, when I got to canyon and canon again (without the heavy emphasis this time), everyone started laughing again. Finally, the light went on for me. I asked, "Is 'canyon' a bad word in Korean?" Several people nodded yes. I asked, "What does it mean?" No answer. I just went on with the rest of the material and finished the class.
After class, I asked one of the girls who seemed to be a good student what "canyon" means in Korean. She seemed pretty uncomfortable. Finally, she said that there isn't an exact translation, but it is kind of like "F--- YOU!"
I just laughed and said, "Oh, OK. Thanks."
As I was walking back to my office, I realized that I had been saying again and again, loudly and with clear pronunciation: "F--- YOU! F--- YOU! F--- YOU! F--- YOU!"
OOPS!!
Ahh - the hazards of teaching cross-culturally!

Also this gives a whole new meaning to America's greatest national park: "The Grand Canyon"!