I work in a high school with many ESL students, and while they do not curse, some of the students do not follow other classroom rules like no cell phones, speak in English, don't play computer games during classes. In addition, some students just resent having to work hard just to communicate in a new language, and I think they take out their frustration on the teachers sometimes. In addition, I am a College Advisor, and when I had to dash the hopes of some students based on their cumulative GPAs that they wouldn't be going to the most prestigious American colleges, I think too that I gained the ire of several students who disliked me as the bearer of bad news. Again, college admissions fills some of them with anxiety and nerves so they lash out in their anxious states at anyone who suggests things may be harder than they expect or they have more work to do than they expect. I don't think high school students are rational or mature enough to handle some of the stresses they face, so the result is that they displace their frustrations onto their teachers.