when you are at work and somebody says something and you want to say "thats what she said" but can't because of people around you. instead, you say the name of your work that way the people you work with understand you but the customers do not.
ted: hey bob, can you hold this package for a bit?
ted: haha good one bob. nice change around.
joe: hey bill I need you to put the special sauce on these buns.
bill : Mcdonalds!
janet: hey john I think I need your help opening the back door.
john: thats what she said!
janet: your fired and I'm sueing you for sexual harassment.
john : damn, should have used a change around.