The One With the Baby on the Bus - S2-E6
Trivia: Phoebe loses her job as a singer at Central Perk. As a protest she sits outside singing for money. Rachel comes out to give Phoebe a cup of coffee. They talk for a while and Phoebe reveals that one of her donations for playing "Smelly cat" was a condom. A moment later a guy comes running to get back the condom, played by Giovanni Ribisi. He's not meant to be her brother, as her brother says when she meets him that he's never been to the city before - just a random incidence of an actor playing different roles across series. (00:18:06)
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