I thought you knew
A Southern way to say 'I agree with you', usually involves tossing your hair like a diva, even if you're bald, and sometimes adds a swear word for extra drama.
'You're gonna fail that test,' he said. She just tossed her hair and said, 'I thought you knew.'
When she said the party was gonna be wild, he tossed his hair and said, 'I thought you knew.'
He said the pizza was bad, and she tossed her hair and said, 'I thought you knew.'