Don’t ever have a concerned look on your face because that will just make them feel uncomfortable. Don’t try to comfort them while stuttering because that will just make them feel dependent. Which will just lower their confidence as an adult. And don’t react differently to whether they stutter or not. And don’t fill in their words out of pity. We naturally fill in each others’ words sometimes, but don’t do it to help them out. Basically, just don’t react to it and if you do talk about it with them, come off like you’re interested in learning about them.