People react different ways in my experience. Most common is this confused smirk they put on their face (which I hate) but people are usually pretty patient. There's the occasional "its ok" or "no rush" type of comment. Im 27 with a pretty severe stutter and Ive noticed that now as an adult, people are more respectful. There's always going to be the occasional dick-wad who laughs but I try to ignore them and finish what I have to say and get away from that interaction before I start taking it to heart, or get angry. I dont stutter when im angry, Lol. But people like this are super rare to come across in my experience.