I can't remember how old I was but I do remember running up to my mom and in a whispered voice saying, "Mom, I can talk to myself." And of course her reply was, "Of course you can." But I was so serious... I just looked her in the eye and said, "No, Mom, I can talk to MYSELF in my own head." And obviously I figured this was something that only I could do and no one else, because I was unique after all.
... she just laughed at me.