It might be an agent (or agents in general), your high school English teacher, your best friend, you spouse, your critique group (or a specific CP), your parents, readers you don't know. Even if you usually have no problem with people reading your work, there's usually someone you dread showing. If you hate showing your work to EVERYONE, there's still someone that's harder, right?
Who is the person you've been most afraid to show your ms to?
For me, it was my hubby. It seems strange now, especially since he reads each chapter before even my writing group reads it. But I wrote for a while--- a couple of years and several books--- before I let him read anything. Why? I was nervous to let him read because he believed in me. YEARS before I even got the first inkling to write a book, he believed I could. From day one, he supported my decision to be a writer. He made sure I had writing time. He'd take off work to be with the kiddos while I went to conferences and classes. He encouraged me to write. I guess I was so nervous to show him, because I was afraid I'd show him that his support and belief in me was misplaced.
Lame, I know. And now I'm really glad I got over it, because I love showing him what I write, and I love his feedback.
So how about you? Who was/is your hardest person to show your writing to? Have you shown them yet?