The One With Joey's New Girlfriend - S4-E5
Audio problem: In the sequence where Chandler chases Kathy down the street, there is a moment, shortly after he walks into the man with the hotdog, where he shouts her name, but his lips don't move at all. (00:11:25)
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