I thought you knew
A catchy song lyric that's like a dumb excuse wrapped in a beat, you say it when you're trying to sound cool but actually sound like a dork.
He said, 'I thought you knew,' and then started dancing like a fool.
She sang, 'I thought you knew,' while walking into the grocery store.
He texted, 'I thought you knew,' and then got distracted by a squirrel.