I don't know anything about that - A way of telling someone you think they're lying and you're

A way of telling someone you think they're lying and you're going to make them feel bad about it.

'I don't know anything about that' said when your sister said she could solve the mystery of the missing socks.

'I don't know anything about that' after your neighbor said he could read minds.

'I don't know anything about that' when your uncle said he could eat a whole pizza in one bite.