This is an interesting one. In my opinion if someone tells you this it will just piss you off, not even just in terms of a stutter. If someone tells you to calm down when you are mad you aren't gonna calm down, you're probably gonna get more mad. You kinda have to come to terms with this yourself, only you can tell yourself to stop caring. Once you actually do not care this whole stuttering thing becomes way easier. If I was to give you one bit of advice is to not give a shit what people think or say to you, YOU DO YOU. Eventually hopefully with that attitude you will be able to relax on your own