Personaly, it just comes naturally. For example, we well talk about idk... The next oral exam in a month. And I'll go : oh yeah don't tell me about it. As someone who has a stutter I can already feel myself getting anxious. Then they'll ask a question or two like did you always stutter or smth. By humor is also really good. Like if someone starts to stutter because we all do sometimes, I'll go : Damn he/she stuttered more than I do and they all laugh. You just want to make it clear to people without having "a talk" about it.