Steve is arguing with his girlfriend, Jane. They have been going out for a little more than two years.
Jane says to him: "I'm leaving you, Steve. Get over it."
Steve replies: "Are you saying that being single will make you happier than you've been with me? Speaking personally, I think the (TOTAL / MARGINAL) utility we've had in this relationship was much more than you could have had if you'd been single this whole time!"
Steve's use of the word "utility" rang a bell for Jane, who had taken an economics class. "It's not that at all. We've had a fine time. It's that the (TOTAL / MARGINAL) utility I would get by continuing our relationship isn't worth it anymore."
Steve replies: "I've never been dumped by someone citing the law of (DIMINISHING MARGINAL UTILITY / SUPPLY AND DEMAND) before. You're a piece of work, you know that?"
Jane doesn't hear. She has already walked off, leaving Steve feeling like something of a sunk cost.