The One With The Embryos - S4-E12
Visible crew/equipment: Near the beginning of the show when Joey asks them who's going to ask the questions a boom mic is visible over Monica's head. (00:05:05)
The One With Rachel's Crush - S4-E13
Visible crew/equipment: When Monica is wafting the smell of cookies to the other in the big apartment, there is a shot of Monica, and all the stage lights are reflected in the TV screen. (00:09:55)
The One With The Ballroom Dancing - S4-E4
Visible crew/equipment: When Phoebe and Rick are sat on the massage table, keep an eye behind Phoebe's head when the camera is on her, particularly after Rick says, "I can always find another masseuse." You can see the shadow of the boom mic moving.
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