(A true story from my friend in the Army)

In this particular branch of the Armys officer training school,
the instructor was returning a test. The students identified their
work by the last four digits of their Social Security number. In the
early hours of a morning, the instructor was calling the numbers.

Four-seven-seven-zero? he asked.
Here, replied one half-awake lieutenant-to-be. Taking the paper, though,
he realized he had mistakenly asked for the wrong paper.

Seven-zero-seven-five? asked the instructor.
Here, repeated the student, gearing for trouble.

I thought you were four-seven-seven-zero, soldier, spoke the teacher.
Thats right, sir, answered our hero. I have a nick-number.