I don’t think this about sharing or splitting the bill though. ‘Dinner’s on me” suggests you are paying the lot. But the cash exchange doesn’t really support this, unless as others have suggested person 2 already paid the whole bill (of $55) in the restaurant. I think it’s the ad that makes no sense - to me anyway. My head is spinning now.That makes no sense.. if we are out to dinner and I pay the bill say its $110 and you apple cash me your half $55... Why would i return your half and then another $55 on top of that?