Conversation which took place in our car this weekend between Second Born and my sister-in-law. Second Born was borrowing SIL's Nintendo DS because he can play in the car without wanting to throw up. SIL can't.
SIL: Are you on?
SIL: You're not me, are you?
SB: No, I'm me.
SIL: But are you actually you? You're not me by mistake?
SB: No, I'm definitely me. I made sure I'm not you.
SIL: Good, because I don't want anyone else to be me.
So that's clear then.