This person is getting on my nerves?

There is this kid in my class who keeps saying he's going to kill me and at the end he is smiling afterward. I try to avoid him to. But sometimes he is at the same place that I met him. He is like pretending he wants to kill me but he never does anything. I never did anything wrong to him and now he is sayng "I'm going to kill you" and then he smiles. Were both teens and males and he keeps acting like that I wonder why he is so annoying?