The One With The Ball - S5-E21
Continuity mistake: When Monica says "Let's go team Monica!" Joey is holding the ball; when the camera angle changes Chandler has the ball and throws it behind him for someone else to catch. (00:18:15)
The One With The Ball - S5-E21
Continuity mistake: When Rachel is outside the coffee shop trying to sell the cat, in between shots, it goes from a standing to sitting position multiple times.
The One With Joey's Big Break - S5-E22
Continuity mistake: When Rachel knocks over the cereal its position changes between shots. (00:04:15)
The One With Joey's Big Break - S5-E22
Continuity mistake: When Joey arrives in the desert there is a lot of stuff not in vans. As the director gets into his car, loads of equipment is still in the desert, but a few shots later the vans are full and leaving. (00:18:50)
The One In Vegas, Part 1 - S5-E23
Continuity mistake: Chandler comes down to find Monica and sees that she's playing some game and having fun. He makes a sad and dejected face. The scene cuts back to Monica, and then to the exact same shot again of Chandler making the sad and dejected face. (00:22:00)
The One In Vegas, Part 1 - S5-E23
Continuity mistake: After Joey tells Chandler about his identical hand twin and plans for getting rich, when he sees Chandler's reaction Joey asks, "Are you unsupporting me again?" while he lifts his left arm and points accusingly at Chandler, but next shot it's Joey's right arm that's up and pointing.
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Rachel is saying to Ross that the pen won't come off, a wheel behind Rachel is spinning or stopped dead in different shots. This includes instant cuts between the 2 angles. (00:12:35)
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Monica puts the blue jumper up her dress, she lifts it up and you can see she is wearing black jeans underneath. The next scene shows her running off without the jeans underneath her dress. (00:18:55)
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Pheobe is telling the Lurker to go away her hand is in the cup of coins, an instant cut later and it's out with no time to do so. (00:29:00)
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Monica and Chandler find the dice under the craps table, it is at an angle so both the four and five appear up. When the camera changes to the last shot (the zoom in of them kissing) the dice is sitting flat on the floor. (00:33:35)
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Monica and Chandler kiss under the table, as "Everybody Loves Somebody" plays, Monica is shown smiling. She then closes her mouth. In the next shot, she is smiling again without any time to do so.
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