Shut up. I am.
Perhaps you are. But I tend to draw people out, so I only see you being shy when you've been treating me as an audience, rather than just myself. When you finish the set piece, you look up, see that it's me, and then draw into yourself as if you just caught yourself running along like a toddler in a department store.
Don't look at me like that! You aren't being anyone else when you launch into a known story! You're being you, but you're being you telling one of your stories!
You're only shy in my presence when your bravado runs out of steam.
Fortunately, that's rare.