Social anxiety is a real condition, and works at a subconscious level. In a state of anxiety, the brain simply does not work optimally.
I deal with it on occasion, even though I'm normally 100% perfectly fine with strangers, groups, etc... But, when I speak in public, and especially when the focus is on me... It's so rough. No amount of practice, conditioning, preparedness does any good when you try to talk and _literally_ nothing comes out. I've found myself having to force speech and it _sounds_ forced in my head. I've never had the presence of mind to ask a friend or colleague what it sounds like to them, I'll have to try to remember to do that next time. I've just always kind of dealt with it because it only happens infrequently that I'm in those situations (1-2 times a year, maybe).
That sounds normal to me. Getting over anxiety requires exposure and most people aren't doing a lot of public speaking on a regular basis. Toastmasters could help with that if it really bothers you.
Yoga and ballroom dancing, especially Tango, are two ways that helped me get out of my mind and tune into my body/emotions/instincts more.
If you want to help him, there's something you can do: Try to practice with him those situations in which he struggles. Start with simple scenarios where you pretend to be someone else and give him feedback about what was weird, when you realized he was blocked, etc. All of this without criticizing or judging him. This way you create a safe environment for him to practice without feeling the pressure of a real conversation and with enough time to understand his own interactions and assimilate them.
I have a friend who is very analytical but gets flustered by many social situations and conflicts. When I ask him what's going on he explains he doesn't understand how to act or what's going on. I've no idea how to help. I've developed instincts, through experience, rather than calculated responses. My instincts can be off and need adjustment over time but it's a totally different way of reacting. Much less taxing on me emotionally than what he goes through. I don't need to think I just need to practise. But this doesn't seem to work for some people and I have no idea why?
I remember in my late teens and early twenties experiencing this but I just grew out of it. How do you help someone develop interpersonal skills and instincts?