This is extremely unusual...should I be concerned?

In my opinion, I think that you should contact one of your school teachers or like mentioned above say something to your guidence councelor. It probably is something innocent but these days you can never tell. That was a good idea concerning the year books. Maybe you can go to the school library and see if they have year books that you can view that covers everyone in the school. If you haven't found him yet and the guidence councelor comes up with zero, it could be your young man may not even be enrolled at that school. It wouldn't be the first time that that has happened. Perhaps he has plans for you. You probably should go into defense mode. It may be he is someone trying to play a crude trick on you but don't take the chance of winding up being a cheeseburger sandwich on his plate. Tell your friends about him so that they can be watching out for him and you. I don't condone this but maybe you should think about the next time he comes up and says something like that throw a fit with everyone watching and I believe he will try to get lost in the crowd like he did before. Take note of all your friends who saw your display and tell them what it was all about and if they would go with you to give descriptions of the boy. I am not trying to scare you. I am trying to get you to be aware of your surroundings so it would be harder for him to approach you. Chances are it is nothing really to worry about but you never know. Say something to your parents so that they are alerted to this boy and should you be late that they may consider going out looking for you. But I do believe you should say something to the school authorities and your parents. I hoped that I helped and did not hinder. Best Wishes - GDH