You should give the $40 to the owner of the ice cream store.
What does that have to do with this?
The Wolf
Just a little joke – my way of saying that I don’t think you owe the money, as I felt on the ice cream question (someone responded to that one that it would be tzedaka).
The majority of the times, my intention when I returned the money it was almost akin to a juvenile (yes, I can act that way sometimes) “tag, you’re it.”
That’s precisely why I don’t think you owe the $ to maaser, but in this case, if you give it to tzedaka, you do get a mitzvah anyhow.