The One Where Rachel Goes Back To Work - S9-E11
Continuity mistake: Ross bends over Emma to kiss her and gets the bow stuck on his head. The bow is slightly over his left eye but in the next shot, it has moved to the centre of his forehead. (00:11:35)
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