When you say abnormal nerve, do you mean it may hurt you? If so, you can consider staying away from him. For example, some unsociable people will attack others when they say something they don't want to hear. In addition to psychological attacks, there may be physical attacks. It's good for you to stay away from such people. If you have to meet him often for special reasons, such as he is your classmate or colleague, you can avoid interacting with him.
At the same time, the nerves in your eyes are abnormal, perhaps just a habit of others' life and communication. Everyone is an independent and equal individual and the center of his own world. Change your inappropriate view of others. When you don't have so much prejudice against others, then some bad emotional reactions to him, such as your fear, will be gone. Try to get to know him, don't just focus on his abnormal nerves. This may just be your prejudice against him. When you begin to trust someone, you will naturally not be afraid.
Besides, you may have amplified your fears. Maybe you've been hurt by someone you think is crazy before, so you're more allergic to people with the same characteristics. In fact, they are not as bad as you think, or they have nothing to fear. You can alleviate the fear of such people through self-cognitive debugging or psychological counseling. I think your psychological factors have a great influence on your fears. In real life, there may be many people with so-called mental disorders in your eyes, and you will always deal with them, so you should change your view of others and look at their advantages.