Hi Mulan,
Thank you very much for sharing this!
I do not think we can judge anybody (you or somebody else) just by their thoughts. We cannot control our thoughts or feelings totally, so, how can we judge you by your thoughts?. I think we can judge people by their acts. So far, you have done nothing to this guy. I cannot see anything bad (or good) that you have done here Maybe I am not paying attention or I do not understand. The good thing to me is that you are aware of your thoughts and feelings, even if they are not perfect. I mean, everybody likes to be "good" and have "perfectly good" thoughts and feelings and does not like to accept or admit that sometimes we have bad thoughts or feelings. You are mature enough to acknowledge that you dislike this guy and that you have thought of cheating your teacher somehow. I congratulate you because you are able to identify those thoughts of yours and communicate them to us.
About this guy, perhaps on top of the features of him you dislike, there is this thing that people have teased you about him; you may not like the fact that some people maybe have found you to be similar to him ? I do not know. If this is the case, it is understandable you feel some rejection for him.
Perhaps, one day, when you feel more comfortable with yourself, you will be able to disregard the stupid comments or jokes of your classmates, and also, you will be able (if you like and want) to act in a compassionate way towards somebody like this guy, who is not very likable and probably has some problems
In the meantime, perhaps you are still young and struggling to find your own identity, to come into terms with the way your see yourself.
I would not worry too much for this episode.
Again, i am happy for you as you are in touch with your thoughts and feelings.