One of the biggest underlying causes of social anxiety can be the belief or feeling that a certain outcome will mean that "I" will die. Not physically, but psychologically.
If the whole room is judging you in a certain way, or laughing at you for something, it is easy to feel as if you are shrinking down to nothing without your old identity to rely on anymore. We feel as if something like that will mean we will lose who we are, as if we are dying in some way. And that can be scary.
The anxiety comes to tell you to keep away from the dangerous situation. All we have to do is see how dangerous it actually is...
A tip for this is to invite what you fear most in a social situation e.g. everyone pointing out and laughing at what you don't like about yourself. Invite it. Imagine it, make it as real as possible. Then see what happens to you in that situation. Are you made less? Do you die? Or are you just standing there, and nothing has actually happened?
If you do that little exercise, make it as real as you can, and do nothing to try to stop "them" laughing or criticising - it might start to remove your fear. Hope that helps.
For more on how to deal with anxiety, check out this page.