1
A smug promise you make to someone who's trying to get you to keep their secret, even though you're probably going to spill it later. It's like saying 'I won't tell if you don't' but with more attitude and less brains.
'I won't tell if you don't,' she said, while secretly texting her best friend about it.
'I won't tell if you don't,' he said, right before he told his mom.
She said, 'I won't tell if you don't,' and then told the entire class.