A Tough Teacher

A school teacher friend of mine injured his back and had to wear a plaster cast around the upper part of his body. On his first day of the term, still with the cast under his shirt, he was assigned to teach the most undisciplined class. Stepping confidently into the rowdy classroom, he opened the window as wide as possible. Just then, a strong breeze made his tie flap. Trying to fix the tie, he took a blackboard eraser and hammered a large tack through his tie into his chest.
He had no trouble with discipline that term.