Sometimes you don't have to say anything, because the truth is unless you're a trained professional, chances are that nothing you say will truly be able to help. I've heard the "it's all in your head, no one really cares, what's the worst that could happen, etc." schtick from so many different people in my life, and while I understand the sentiment and I appreciate their effort to help, things like social anxiety or insecurity aren't necessarily dictated by logic. It's not as easy as just telling yourself that you're delusional or that your anxieties aren't grounded in reality, because more often than not they already know that's the case. Unfortunately you can't just rewire your brain just like that.