The One with the Fake Monica - S1-E21
Trivia: When the fake Monica meets the real Monica in the tap dance class, Monica says she is Dutch. The fake Monica says: "Mag ik deze dans van jou?", which is Dutch for "May I have this dance?".
The One with the Fake Monica - S1-E21
Trivia: In the scene where Ross has just explained to Joey & Chandler that he has to give up Marcel, there is an advert break. Immediately after the break, the shot shows the three guys sitting on the sofa in the coffee house. If you look at the positions that their hands are in, they are mimicking either "See no evil", "Hear no evil" or "Speak no evil". I think this was done deliberately but since there isn't much laughter, I don't think the studio audience spotted it.
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