The One With The Ball - S5-E21
Other mistake: The guys start the ball-throwing game at around 2 in the afternoon. Later, they mention that it's been going for 10 hours, making it around midnight. Why would Rachel, who never cooks, be defrosting a chicken? And why would she be doing so at midnight?
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