Happens to me and I'm sure others from time to time. I've gotten used to it and think to myself, " I very well could be the very first people they have encountered to has a stutter." I try to think our interaction could have served as a lesson for them and that maybe the next time the customer with the stutter will have less patients and the employee with be able to remember our encounter and be more understanding. After I encounter something like this, when I'm done with my order or whatnot I just mention that I have a stutter and this is just the best I can speak... Usually get an apology and a shameful expression from whoever helped me. It sucks but then again, I know many people who tell me that I am the first person they have met with a stutter.