I think that most listeners are unfamiliar with stutters, and they can see you are in distress - they are just trying to help. Sure, some people are doing it because they're impatient jerks - but I find if I tell people that I have a stutter, they back off and let me finish. And if they keep trying to complete my sentences, I tell them that that makes it harder for me. ​ For years I felt like everyone was just being inconsiderate - I hadn't thought about how this is new to them, and things that are obvious to me, they would have no way of knowing. It's frustrating, I know - but I look at it as "well, at least I'm educating them for the next stutterer they meet!"