fact guaranteed
A 'fact guaranteed' is like a swear-filled guarantee that someone is 100% sure about something, even if they’re totally full of hot air.
'You’re gonna fail this class,' he said, like he had a degree in failure.
'I’m gonna win this game,' she said, like she had a trophy in her pocket.
'You’re gonna eat that whole cake,' my dad said, like he had a dessert contract with my mouth.