You will always encounter assholes and sometimes good people who don’t make it an issue and even people who may say or make strange faces only because they are uncomfortable. There’s still a lot of progress to make in terms of educating people and even advertising for ourselves to let it be known that we stutter whether on a personal or macro level. For people like this I don’t feel bad for making them look and feel like they were an asshole. In this situation you could have either ignored it, said that you have a stutter or even go to management and report it. Never beat yourself up about it though you did a great job of keeping your composure