Your sub-conscious is not letting you be relaxed in those situations. It has learnt over many-many years of avoidance behavior that the situation is not 'safe'. The reason it is so difficult to overcome this sense of fear and anxiety is because you can't really 'control' your sub-conscious (thats why I scoff at people that advise us to not think about stuttering while speaking .. like how? We cannot control our sub-conscious thats doing the thinking!!!!!). Only way to truly overcome this is, little-by-little train your sub-conscious to 'forget' this negative behavior, and retrain it using positive feedback. It takes time, proper guidance and consistency. Some people can achieve these on their own, most need help. I've been retraining my sub-conscious for about a year now with help of a coach, I'm now able to overcome most of my anxiety, and subsequently overcome my stutter in these situations. I can now hold conversations with strangers and at work without 'thinking' about stuttering, which allows me to relax. I'm still working speaking in front of big groups. I'm hopeful I'll be achieve this by another year or so. DM me for more details