At the start of the exam, the invigilator says,
“You have exactly 2 hours. I will not accept any papers after this time has elapsed.”
Two hours later, the invigilator calls out,
“Time’s up, Ladies and Gentlemen.”
Little Johnny is still scribbling away ten minutes later when the invigilator has all the collected papers in a large stack in front of him.
Slowly, Little Johnny finishes up and walks over to hand in his paper, but the invigilator refuses to accept it.
Little Johnny puffs up his chest and says:
“Do you have any idea who I am?”
“No,” says the invigilator.
“Great,” says Little Johnny as he slips his paper into the middle of the stack.