How to deal with a student who harasses the (inexperienced) teacher during class? I am a young teacher at college. I have to go way too long, I know but I have the following problem. 

In one of my classes, I have this guy who pecks at me for everything I say. He is surely conceited, but it hurts like hell when he makes fun of me in front of the whole class. 

However, I take no note of it in class, but later I feel very sad. This makes me frightened to go to that class at all. 

He is overconfident and imposing and seems to have got a big gang behind him. He is a threat and he disturbs me. Please help me tackle this situation.
As a first step you could ask one of your more experienced colleagues to observe your teaching. Let the students know the colleague is there to evaluate your teaching. While it is obviously not a formal evaluation, it is an evaluation of how you handle a difficult teaching situation. You want to tell the students that you are being evaluated so that the trouble makers feel like they can sabotage you. If they do not know why they are being observed, the trouble makers may behave better. The goal is not to "catch" the student behaving badly, it is to have an example of bad behaviour so you and the evaluator can work through possible responses after the class.

Hopefully the trouble makers will try and "undermine" you and act out. With first hand knowledge the colleague may have specific suggestions of how to deal with the student. If the student does not act out you can then discuss the types of behaviour the student shows with the colleague.

Ideally the observer would be from your department, but if it is difficult to find someone, the observer does not need to be from your department nor understand the material you are teaching. They do not need to commit to the entire lecture, 15-30 minutes is often enough. The key thing is they need to be experienced enough to be able to provide suggestions and someone you respect enough to take the suggestions on board. If they understand the material even better, but you want someone that you respect with the needed experience.