A statement which started as a joke,but which evolved in many interesting ways, my favourite being as a method of absolution.
E.g."Terrance, if you're not going to shut up, you're going to have to leave the room."
"It's not his fault miss, his dad's on crack."
It was used so often that people started to believe that Terrance's dad WAS actually on crack, and things got so bad that Terrance's dad eventually felt the need to pay a visit to our class. He explained that he was not on crack, and was actually a factory worker. We all remained silent throughout the speech, until my friend Nick raised his hand.
"Yes?" said Terrance's dad.
"How can you afford to raise a family and keep up a crack habit on a factory worker's salary?"