I've been followed.......?

This days, I'm now in a big university campus building.

Recently, in one of my subjects for only once a week and we students enrolled in this subject are many and we use the university gym as our classroom. Then a guy sat down next to me who have a different code smiled at me but I don't know who he is. During the class, he kept looking at me and smiling like he's a maniac or a retarded. He kept looking at me for the entire time and I don't know what to do and I don't want to shout at that time because of the crowd!

When a teacher told a joke in front, I and my girl seatmates and classmates laugh together and at that, he continued to laugh and looking at me as if I'm laughing with him. I don't even know who he is and he kept pushing himself to sit beside me as I was trying to avoid him! And I can't forget that! I want to tell it to my adviser but I just don't want to because I lack proof and I don't know if he's a retarded abnormal person.

By the following days, I already had a trauma of that guy and he seemed to familiarized my face and even seemed to follow me. One time, this Thursday as me and my girl classmate were sitting there waiting for the time for our next subject, we're talking great and after that, I sense that somebody is sitting beside and I look who it is and it was him! I've told this dilemma to my classmates who are close to me but I have no proof to tell to my adviser because he seemed to be a normal when I see him on our once in a week class. But the problem is that he looks at me and also to others like a retarded person!

Can somebody tell me if he's really a retarded or a maniac?