The One With The Memorial Service - S9-E17
Continuity mistake: After Phoebe kisses Mike in her apartment, Mikes friend rushes in and discovers them. As soon as the shot widens, Mike's hand moves from being behind Phoebes head to his lap. (00:17:35)
The One With The Memorial Service - S9-E17
Continuity mistake: In the beginning when Joey tries to spin the ball with his finger, it falls, hits the table and bounces to the background. In the very next shot it is seen falling behind Chandler on the couch.
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