I forget where but there is someone on here who does make them up. I can't think of the name but if you search you'll definitely find him. If I think of it or find him I'll send the link, but there definitely is someone on here who does good ones from what I've seen.
What do you want to be when you grow up son?
I want to be a fireman!
Sorry, you can only do one or the other: Grow up or be a fireman!