Bill is a 12 year old boy. His mom has a very bad job- people pay to have sex with her.
One day while Bill was in school, he was talking with his best friend, Joe,and suddenly asked Joe what he did last night. Joe replied "I did your mom" and Bill said "Eeewwww!" but then Joe continued "a favor" "Oh good!" "by making you" "Nooooooo!" and fianally Joe said "a sandwich". "Wait," said Bill,"you did my mom a favor by making me a sandwich?" "That is correct," answered Joe.
"wow! that was close! for a second there, I thought that you had sex with my mom."
"Oh! Yeah... I did that too."