The One That Could Have Been, part 1 - S6-E15
Continuity mistake: In the scene where Joey gives Chandler the orange juice and says sorry, the paper cup's logo faces Joey's hand, then the shot goes to Chandler and when it comes back, the logo on the cup faces Chandler. (00:15:15)
The One That Could Have Been, part 1 - S6-E15
Revealing mistake: In the opening credits for both parts, fat Monica jumps on the couch and it lifts up on Chandler's end. If you look carefully at Chandler, you can see him holding one end of the couch with his hand and pressing up with his foot. (00:02:10)
The One That Could Have Been, part 1 - S6-E15
Continuity mistake: Near the start, Chandler is sitting in the coffee house in the big chair. When he's talking to Joey about money, his feet change positions every two seconds. On the floor, crossed, resting on the table, the list goes on and on. (00:04:55)
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