The Teacher was asking the kids to explain different punctuation-marks.
When she got to Johnny (knowing better) she asked him, "What's the most important puntuation-mark?"
Surprisingly, she got what she figured was the correct answer: "A period, Teacher."
Smiling, for once having a decent answer from her most troublesome student, she made the mistake of asking, "And WHY do you think a period is the most important one?"
Johnny shrugged. "Beats me!" he replied. "But it must be awful important; because when Big Sis said she missed one, Mom had hysterics, Dad fainted, and the man next door shot himself."