I don't even know what that means
You say this when you’re so clueless you think the sky is pink and you're too lazy to check.
He said, 'I don't even know what that means,' after I told him about gravity.
She said, 'I don't even know what that means,' when I asked her what a letter was.
He said, 'I don't even know what that means,' after I explained what a clock was.