I dont know where you're from. But most people dont understand whats going on, so if you calmly explain to them that you have a stutter and cannot control it, 99% will probably feel bad and apologize. In almost every case of laughing i know of, it's due to a lack of knowledge, i.e. ignorance. Which isnt their fault if they dont know about stuttering. Explain it to them in a normal way and show that you are comfortable with it. that usually works.