I owe you one - A promise that you’ll do something nice for them later, but

A promise that you’ll do something nice for them later, but only if they don’t remind you every single day.

You said you’d buy me lunch. Now I’m texting you at 11 p. m. about it.

I’ll pay you back. Probably. Maybe. If I remember.

I owe you one. That’s what I said. Now I’m stuck with your debt for life.