When I was in college, I worked at the college bookstore. One day a girl came in, took a pen off the shelf and brought it to the register. Then she took an old pen from her pocket.
“I used up all the ink in this one,” she said, indicating her old pen. “Can I trade it for this?” She pointed to the new one.
“What?” I said.
“Can I give you this old pen, and you give me this new one?”
“Is this some kind of sociological experiment or something?” I asked.
Turns out it was. And I ruined it.
I didn’t give her the pen.