The One Where Monica Gets a Roommate - S1-E1
Trivia: In many of the first episodes, there is a beam going from the ceiling to the floor in between the kitchen and the living room. You can see it when they show the door. In "The One With The Giant Poking Device" Ross actually runs into it. In the majority of the later episodes, the beam is non-existent. The beam became the trademark for director James Burrows. Whenever he returned to direct an episode, the crew intentionally added the beam.
The One Where Monica Gets a Roommate - S1-E1
Trivia: Phoebe singing giant pigeon was a deleted scene from the pilot. When it was used years later in DVDs with extended footage the audio was not very good and they had to get Lisa Kudrow to redo the audio. (This information can be heard on extended DVD audio commentary for the pilot).
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