man that's a really inappropriate comment that that guy made... I used to teach, and when my new students made joking-but-not-okay comments like that, I got really good at taking a deep breath, making a sad-serious face, and explaining that I had a stutter and sometimes had trouble pronouncing some words. The sad face and complete lack of anger would turn the discomfort on THEM and they never did it again - def better than laughing it off, but hard to collect yourself in the moment sometimes