Most of my friend group ,if not all, know I have a stutter I usually have an open transparency about them with it ,so when they crack a joke I usually laugh with it. If it does happen with someone I don’t know of I just don’t give two fucks about it and move on with my life and not worry about it. I see it like this, if they is going to make fun of someone’s speech to seem funny or have a laugh they are just toxic people and you shouldn’t keep their toxicity in your head throughout the day