The One With The Dollhouse - S3-E20
Continuity mistake: When Chandler's in Rachel's office, she tells him the lingerie isn't kept there. He says, "Yes I realise that", and starts reaching for the catalogue she's about to give him. Camera cuts, and he's now standing with his hands in his pockets, reaching out again when she gives him the catalogue. (00:02:40)
The One With The Dollhouse - S3-E20
Continuity mistake: When Monica and Phoebe are looking at the dollhouse, Monica says "I don't want a ghost for the house." When she says this, the camera is behind Phoebe whose right hand is up in the air. The shot then changes to Phoebe from the front, and her hand has instantly gone to her lap. (00:04:40)
The One With The Dollhouse - S3-E20
Continuity mistake: When Monica is telling Rachel that guys always say they are going to call, but it doesn't mean they will, she is eating yogurt; in the next shot she has a cup ready to drink out of. (00:14:30)
The One With The Dollhouse - S3-E20
Continuity mistake: After Joey walks away from the understudy and sits at the table, his hands are on the table but not touching; they are touching in the next shot. (00:07:50)
The One With The Dollhouse - S3-E20
Continuity mistake: When Joey is talking to the understudy, he is holding a cup. It disappears right when she invites him for a drink. (00:07:20)
The One With The Dollhouse - S3-E20
Other mistake: The dollhouse is only partially burned when Ross takes it into the bathroom to extinguish it. When he shows it to Phoebe it's completely blackened and destroyed. He and Monica wouldn't have just let it burn; they would have extinguished it ASAP, and there's no reason why that wouldn't have been fast if they doused it in the shower.
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