One thing that helped me, especially in dealing with group meetings or class presentations is this:
Generally, people do want to like other people. And they do have empathy for other people who struggle in situations we find difficult. At first, it might not help your confidence, but it might make you more at ease. It's a step in the right direction.
And if your around people that seem to intentionally make you feel insecure, I would deal with them as little as possible (if at all).
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“There's only one rule that I know of, babies - God damn it, you've got to be kind.”― Kurt Vonnegut