The One With Princess Consuela - S10-E14
Continuity mistake: After the scene Mike and Phoebe are arguing about changing their names in Central Perk, just before Phoebe meets one of her clients, a purple cup disappears off their table. (00:19:40)

The One With Princess Consuela - S10-E14
Continuity mistake: After Ross announces his tenure, when Rachel starts crying and tells him that she got fired and didn't get the other job, her right hand is up by her face, but in the next shot her right hand is holding the glass of champagne and it's her left hand up by her face.
The One With Princess Consuela - S10-E14
Continuity mistake: When Ross hugs Rachel in Central Perk, after finding out she has been fired, he leans his face against hers twice.

The One Where Estelle Dies - S10-E15
Continuity mistake: When Chandler says his boss is getting him a new lamp in his cubicle, his arm is over the back of the chair, in the immediate next shot it is moved and then back again. (00:00:50)
The One Where Estelle Dies - S10-E15
Continuity mistake: Just after the opening titles cut to Central Perk, four people can be seen having a conversation through the window. In the next shot, there is one person sitting next to the window and a waitress has appeared out of nowhere. (00:03:05)

The One Where Estelle Dies - S10-E15
Continuity mistake: The second time Ross visits Mr. Zelner, he hands him a pterodactyl egg replica. The hole in the egg switches between the top or bottom, depending on the shot. (00:14:40)

The One Where Estelle Dies - S10-E15
Continuity mistake: Near the end when Chandler is talking to Janice at one point his hands go from pointing straight ahead to his pockets. (00:17:20)
The One Where Estelle Dies - S10-E15
Continuity mistake: When Rachel walks in with Emma, Ross is on the laptop. It is straight and on the table, in a later shot,the laptop has moved and is over the edge of the table. (00:18:50 - 00:20:55)

The One With Rachel's Going Away Party - S10-E16
Continuity mistake: The level of beer in Ross' bottle goes up and down between shots as he's talking to Joey at the kitchen table. (00:12:00)
The One With Rachel's Going Away Party - S10-E16
Continuity mistake: When Ross fears that Rachel is going to talk with him, the volume and the color of his beer changes between shots.
Continuity mistake: When Ross and Rachel are standing at Ross' door after Rachel comes over to say goodbye and they are hugging and talking, Ross' right hand changes from being on Rachel's shoulder to on her waist and then back to her shoulder. (00:00:35)

Continuity mistake: When Chandler and Monica are in the birthing room and they have just been told they are having twins, her scarf keeps changing from sitting on her shoulder to being over her shoulder. (00:10:20)
Continuity mistake: When Ross is talking to Phoebe and Joey in Central Perk, a strand of Phoebe's hair keeps getting snagged behind the buttons of her blouse and hanging loose again with her other hair several times during the scene. (00:12:40)

Continuity mistake: When Chandler and Monica are at the hospital holding the twins right before they try and swap babies, there are two hospital tags around Chandler's left wrist which then disappear before re-appearing. (00:15:25)
Continuity mistake: When Monica and Chandler walk into the apartment with the twins, 2 very bright yellow soothers keep appearing and disappearing from the babies' mouths. (00:18:50)

Continuity mistake: While Mama Joey is looking for Chick Jr. and Duck Jr., the things pinned to the bulletin board beside the door have vanished when Monica and Chandler walk in, but after Monica walks out to check on the twins everything's back up on the board like it was before.
Continuity mistake: In the hospital when Erica is giving birth and the camera is on the doctor, the door to the room is closed. However, when the camera angle changes, the door is wide open even though no one had entered or exited.
Continuity mistake: On the plane, when Rachel says "She's almost never right," (about Phoebe) you can see the guy's hand is on the armrest. Then a split second later, his hand is about half a feet off the armrest while saying "But she is sometimes." (00:15:15)

Continuity mistake: When the friends put down their keys, the keys' positions change when the camera pans the apartment. (00:25:30)

Continuity mistake: When Phoebe's driving Ross to the airport in her cab the rear view mirror vanishes from the windshield, then it reappears and disappears again. Additionally, when they start their drive the cab doesn't have a side view mirror on the passenger side, but en route the cab has acquired one, then it vanishes again.
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