The One With The Inappropriate Sister - S5-E10
Continuity mistake: Ross and Joey are discussing Joey writing his own moviel; Ross sits down to begin writing, and Joey places a beer on the table next to him. The large part of the label is facing to the side, but it then switches to facing the front without being touched. (00:06:20)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: When Rachel and Monica are arguing about her meddling, Monica raises her hand to her face and you see a sparkly engagement ring on her finger. Her character wasn't engaged but Courteney Cox was at the time. (00:07:05)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: Joey and Chandler are playing 'Fireball'; Joey puts his hand through the wall next to the fridge, then in the next scene the hole is gone with no trace. (00:08:50)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: Rachel goes into Danny's apartment and we see that his door opens up right into his living room. However, in "The One With The Yeti", we see Danny's apartment from outside the door and there is a wall directly behind him. (00:11:00)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: Phoebe is complaining about people disrespecting her charity bucket, and hands the bucket to Monica as she does so. In the first two shots Monica holds the bucket by its edge, but when the camera goes back to her for a third time, she is holding the bucket by its handle. (00:11:35)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: When Phoebe is being removed from her "bucket spot" she starts to take off the signs she has put up. With the camera close up to her, she rips one off, then the camera changes to a wide view, and she is suddenly holding two signs. (00:16:40)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: When Joey and Phoebe are talking to each other on the couch, Rachel tucks her hair behind her ears, but in the next shot it's moved.
The One With The Inappropriate Sister - S5-E10
Continuity mistake: When Joey is talking to Ross about him being an actor, the shot changes and Ross is holding his beer in a different position.
The One With The Inappropriate Sister - S5-E10
Continuity mistake: When Rachel and Monica are talking about Danny and the girl on the subway, Rachel has tiny bits of her fringe hanging out and it moves between shots without any movement.
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