It's not my usual policy, but sometimes I have kids who pay me once a week, in cash. Today's transaction provided much more levity than usual...
KID (handing me a payment): Here ya go.
ME: Woo hoo--lunch money!
KID (ponders that for a second): Lunch money. Man! Sixteen whole dollars. You must make a fortune. Sixteen dollars a day!
I'm pretty sure he seriously thought that was a lot of money. But I did successfully manage to explain to him that I made more than $16 a day (because I teach more people than just him), I told him the total number of people I'd be teaching today. He then proceeded to do the math (on his hand, with a pen), and, after computing the total, came out with this gem: "Oh, man--I'm gonna have a sweet side job when I get older!"
(He also noted that he would do this as far away from here as possible, so he wouldn't have to compete with me. Heh.)