fact guaranteed
A 'fact guaranteed' is when someone says something with such force it sounds like it's gonna become law. It's like they've already signed the paperwork and you're just the witness.
'You're gonna get a zero on this test,' he said, like the teacher was already grading it.
'I’m gonna be the best in the class,' she said, like she had a golden medal waiting.
'You’re gonna eat that whole pizza,' my brother said, like he had a pizza contract with my mouth.