A family was all together recently, just hanging around. The sister was browsing through an almanac and laughed at a little piece of trivia she had found in the book, which she then read aloud; "Did you know that a woman's breasts increase in size by 25% during sex?"
The brother-in-law, a notorious joker, shot back, "So, how come yours
To which the father, from behind his newspaper and without even a pause,
replied, "You're not pumping hard enough."