The One With The Ballroom Dancing - S4-E4
Continuity mistake: In the Central Perk scene when Joey is telling Monica and Rachel about the dancing, Monica's legs are crossed left over right and then right over left, and back again. (00:10:55)
The One With The Ballroom Dancing - S4-E4
Continuity mistake: While Treeger chews out Rachel for not properly disposing the pizza box in the trash chute, the room's door is closed, then wide open, and then closed again.
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