KID: Would you like to buy some candy to help my church?
ME: I'll have to use that lame-but-true teacher excuse in this case: if
I bought something from you, I'd have to buy something from everybody.
KID: But not everyone here goes to my church. (points to kid across the hall from him) This guy hates God!
(He was kidding, of course, and the alleged God-hater took the joke in good fun.)