I am teaching English as a foreign language in Taiwan. My students are college non-English majors, yet most of them speak fairly frequently. I notice that two or three of them often speak quite rudely during in-class discussions, saying sentences like "I don't understand why we need to talk about this" and "That's stupid" and "Yeah, big deal" and "So what?" (with a very challenging tone), to their classmates and to me. I can understand that they probably their English from movies, which is not entirely a bad thing, but I also believe that they should understand how to use their language appropriately in academic settings. What should I do? Thank you.

Joe