"How many have sex, on average, five times per week?" More hands.
"Three?" Now the hands dwindled.
"Once per month?" No one.
"Once every three months?" No one. "Once every six months?" No one.
"How about once per year?" One man near the back jumped up and pumped his arm in the air, yelling, "Me! Me!"
The professor said, "Sir, I appreciate you rounding out the curve, but why are you so proud of having sex only once per year?"
The man yelled, "Because tonight's the night!"