My guess is maybe your jealous that you don't have the confidence to do what he does. I don't know, but whatever the cause may be you need to stop immediately. As a stutterer you should be able to empathize with what he's going through. I had a presentation a couple weeks back in school and let me say it was terrifying. I only stuttered a couple of times but it was still very embarrassing. My tip is to work on your empathy and control you impulses. And don't be that douche. good luck