I don't even know what that means
You use this when you're pretending to be smart but you're really just trying to hide how much you sucked at the conversation.
He said, 'I don't even know what that means,' after I asked him what a metaphor was.
She said, 'I don't even know what that means,' when I told her I got a perfect score on the test.
He said, 'I don't even know what that means,' after I explained what a cell phone was.