I'm using voice to text here so I hope this comes through okay but I am a college professor* and I have had a few students in my classes who have stuttered and it is Beyond unconscionable that he would last at you sure he may have thought it was a joke but even so if you were joking about stuttering that's an inappropriate thing to joke about and therefore he should not have laughed. I won't tell you your business but I would encourage you to consider speaking to the chair of the department about what had happened now most certainly that would be escalating this to a level that you might not want but that type of behavior just simply cannot be tolerated! * I still stutter a bit - i mainly have blocks (and it occurs in class). I have no recollection of ever being laughed at due to my stutter but most certainly when I was younger perhaps it occurred I can't imagine how angry and frustrated you were for the rest of that class