I sympathise with you. It also doesn't help when people tell you that you're (over)sensitive and need to 'deal with it' when I feel and express concern about a particular student. When I feel like this (often but I 'sit on it', in order to avoid 'making a scene' and 'keeping control of the situation'), the first thing I do is remind myself that I have every right to feel this way and it's because I'm a caring and hard-working person who wants to do well and wants my students to do well because I know how hard it will be for the student later on unless they get things right now. The second thing that I remind myself of (and this isn't arrogant) is that:
1. I've got what this student needs-An A-level/degree/masters/doctorate etc (depending on the course I'm teaching) and the student is there to learn from your knowledge and your experience.
2. Regardless of what the student does, I will still get paid just for turning up. The student can muck around all lesson, but because I'm in the room, I'll still get paid, so it's not my time or future that the student is wasting but his/her own. Moreover, if I know that I'm doing everything I can to the best of my ability then there's no need to be agitated.
3. I can get a job that I enjoy more easily than the student can because of point 1. This point sounds cruel but helps me to put the situation into perspective and stop blaming myself for the student's problem.
4. It's the student's problem not mine, unless I react to it in a way that I regret (e.g. 'giving the student a piece of my mind in front of the whole class'). Also, it's not possible or my job to make every single student learn and enjoy it as much as I do (if that happens great) but in reality, even if only 1 student feels like this then I've made a huge achievement.
The third thing I do is express/vent my anger in a safe environment. E.g. I let rip about what a so and so the student is in my teaching diary (kept under lock and key of course) afterwards or take a walk etc (in the actual lesson, I might take a deep breath and either excuse myself for a few minutes or get the student in question to leave the room on an errand for a few minutes, in order to give myself some breathing space), then I ask myself why I'm angry. In my case, it's frustration and self-criticism/doubt because I think that it's my fault he/she doesn't want to learn and is mucking about and I'm cross with the student for causing me this problem and cross with myself for being unable to do anything about it. Once I'm aware of this, I think about ways I can deal with it. E.g. I feel better about what I'm teaching if I've prepared the lesson well or tried to do something that I haven't done before or I've had a laugh with the students (I know that your type of course is different to A-Level Psychology, this may not work for you).
Finally, I spend a few minutes thinking (once I've calmed down) about why the student is mucking about. E.g. Is he/she finding the work difficult? Does he/she have problems at home or a demanding job? Is he/she really intersted in the subject or just doing the course to please someone else (e.g. parents)? Does he/she have a learning or behavioural difficulty which makes life harder for them? If I can, I also have a chat with the student (e.g. what do you think of the course? What do you want to do next?) either during the lesson (if possible) or call him/her aside at the end after giving back work? I also talk to other colleagues about the student and ask how the student behaves for them and how they cope?
I hope that this answer helps!