I was recently teaching at a school where there was a group of mean girls....just mean, mean to anyone and no one knew when they would turn on someone. When they wanted they could be very sweet but when they didn't they were vicious. Most of the kids were amazing. I looked at the group one day when they were being disrespectful and said told them I wasn't there to be their friend and I didn't care if they liked me or not I was there to do a job and I expected them to do what I said. After that they were always respectful to me. and even began to like me Sometimes they just need to know they have no power over you in their behavior. When you shut it down they often times stop.
As a person I hate to not be liked but as a teacher I hate for a situation to keep others from learning who want to learn. It's about doing my job and providing a good learning environment. I hope this helps!