It's not actually weird but very common in people who stutter. You describe really well how you can be pretty fluent with friends and people you know but not with strangers or large groups. The more comfortable you are, the less likely you are to stutter. Stuttering starts in the brain but if you are anxious your body will add a lot of muscle tension to it and will make it much bigger than the initial little brain blip. Over years and years of stuttering, you have developed layers and layers of habitual behaviours as well as negative thoughts and beliefs around your stutter. Every time you have a block when talking to a stranger, that negative belief is confirmed and becomes more ingrained. Every time you are pretty fluent with friends, your positive belief that you can be fluent with them is confirmed. The interesting thing is that these beliefs are just that: beliefs. They are not truths. It is possible to retrain your brain, get rid of your entire belief-system and be just as fluent with strangers as you are with friends. This won't happen over night. Because we know what an important role beliefs play in managing someone's stutter, we have made this part of the stuttering app we are developing. The app will be connected to a Fitbit-type belt that is worn around the chest. The device records breathing and speaking patterns and gives real-time feedback to the user to encourage him to use his technique, to remind him to practice and to generally encourage and motivate.