Ex has serious staring problems

Ok my ex is getting really really annoying hes being an jerk to me and he keeps making excuses 4 why he needs 2 tlk 2 me. Im trying 2 ignore him and every day when I walk by him and his girlfriend, with my boyfriend he stares the whole time and he will like grab his girlfriend and pull her closer 2 him. Its really ridicuous, and its really pissing my boyfriend off. He says he wants 2 punch his lights out for it, but I can deal with him staring at me in the hall way. but he is also in one of my classes and he actually will turn and sit sideways in his desk so he can look back and stare at me. He doesnt say anything, he just stares. The other day the teacher noticed this and told him that he had to sit in his desk facing forwards with his feet under his desk. So he turned a little bit so that his feet were under his desk and still strained his head back 2 look at me. Its getting really really annoying, and I try 2 ignore it but then he will start like coughing really loudly or singing trying 2 get my attention I guess. Its really hard 4 me 2 concentrate when hes doin all this stuff, anyways does anyone have any advice as to how I can get him to stop. I already ignore him and I am very cold to him when he starts to tlk to me. Just please how did I get him 2 stop staring, its driving me insane.