The One With Frank Jr. - S3-E5
Other mistake: Chandler tries to open the door that leads to his room, but Joey has sawed the door in half so only the upper half opens, and Chandler then falls over the bottom half. He has to hit it with some force to fall over it, but it doesn't budge an inch. (00:00:50)
The One With Frank Jr. - S3-E5
Continuity mistake: In the scene where Joey and Monica discuss changing her bathroom tile, Joey moves the hamper to the middle of the doorway and when he kneels down to measure, the hamper is back against the wall. (00:06:25)
The One With Frank Jr. - S3-E5
Continuity mistake: When Phoebe is talking to Monica while Frank Jr is doing karate on the balcony, the blue cup in front of her moves, disappears and is back again. (00:10:20)
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank Jr. holds a white sheet around himself, while talking to Phoebe about how she really is a masseuse, etc., the gathered sheet in his hand keeps changing repeatedly throughout the scene. (00:14:10)
The One With Frank Jr. - S3-E5
Visible crew/equipment: After Joey nearly drills a hole into Chandler he heads over to Monica's to get a beer, and just as Joey walks into the apartment the camera can be seen at the left side of the screen.
The One With Frank Jr. - S3-E5
Other mistake: Monica doesn't realise what the floor looks like under the hamper, but due to her obsessive cleaning she would know this for sure.
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank has the towel wrapped around him, the knot on his chest changes a lot between shots.
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank is trying to melt a spoon there's one shot where he holds the spoon high above the table, then the angle changes and he's pressing the spoon against the plate.
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