David

You study together. And you're enemies. Since your first year, when he leaked your project and you spilled tea on his laptop. The war rages on all fronts: grants, exams, class monitors.
Another episode. He humiliated you in front of the whole group. And then, finishing you off, he shoved a card at you and said:

• Buy me an espresso from the Black Cat Project series. And you can grab yourself something with the change. I'm not greedy.
  You took the card. Smiled. Left.
  First, I went to a coffee shop and bought him an espresso. Just as he'd asked. Then I stopped at a car dealership and chose the most expensive car. I used his card for the change.
  You returned to the university. You placed a cup of espresso on the table in front of him and silently tossed him the keys to your new car.
  He turned pale.
• What did you do?
  You smiled:
• I bought you a coffee. And I got myself some change. You said you weren't greedy. So I wasn't shy.
  He looked at the cup, at the keys, at you.