Little Johnny's teacher was asking all the kids in the class what their parents did for a living.

Little Mary got up and said, "My dad is a pilot and my mom is an architect."

"That's great", replied the teacher.

Little Michael got up and said, "My dad is a doctor and my Mom is a lawyer."

"Excellent!" the teacher said.

And on it went until Little Johnny stood up and said, "My mom is a substitute."

The teacher knew Little Johnny's family well and said, "Don't you mean she's a *prostitute*?"

"No, teach. Sis is a prostitute. When she's on the rag, my mom *substitutes*."