It's totally your choice whether you disclose or not, but I sense mix signals and contradictions. You "kinda figure" and "assume" your friends would bring it up/know that you do, but you also actively try to avoid your stutter and pretend it does not exist. So, i don't know if you can really come to the conclusion that they know. If I was your friend and I did in fact know that you are stuttering (if youre mild, they can think it's a multitude of things), but I saw you uncomfortable with it, it would make me uncomfortable bringing it up. If everyone knew and understood what stuttering is, we would get a lot less, "did you forget your name?"