YES! omg I have yet to meet anyone who has this experience too. I am nearly fluent with strangers (most of the time) but have a DRAMATICALLY more severe stutter with family, friends, and significant others. My stutter has been this way for as long as I can remember, and it's made speech therapy very difficult because I'm usually fluent in clinical settings! I agree that I think it has something to do with letting your guard down and being relaxed.