I thought you knew
When a know-it-all asks you a question and you roll your eyes and say 'I thought you knew' like they're the dumb one.
He asked, 'What's 2+2?' I said, 'I thought you knew.'
She asked, 'What time is it?' I said, 'I thought you knew.'
He asked, 'Who won the game?' I said, 'I thought you knew.'