The One With Rachel's Book - S7-E2
Audio problem: Chandler, Monica and her parents are at dinner to discuss the upcoming wedding. When they describe how they remodeled the kitchen when she broke up with Richard, the camera pans to Monica and her mouth is moving but there's no sound. It then switches camera angles and Monica audibly asks, "Well what about when I started dating Chandler?" Which is what she said in the frame before with no sound. (00:11:00)
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom