The One Where Ross Moves In - S5-E7
Continuity mistake: When Chandler and Joey walk into the apartment to find boxes all over the place and also when Chandler talks about the air purifier, the door to the bathroom is open and the toilet is right beside the tub (odd that it's there in the first place), but when Joey tells Chandler he wants to play foosball and also when Joey's wearing the helmet, the prop toilet has vanished.
The One Where Heckles Dies - S2-E3
Visible crew/equipment: After Monica yells "Stop with the broom, we're not making noise," when both Monica and Rachel stomp their feet the studio lighting can be seen at the top of the screen, over Ross (this doesn't refer to Monica's star light fixture). And when the others join in stomping their feet, we can also see the boom mic dip into view.
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.
The One After Joey And Rachel Kiss - S10-E1
Visible crew/equipment: Ross, Joey, and Chandler are chatting in the plane. After the camera zooms out when Chandler heads to sit next to Monica, a cameraman holding a camera is visible on the left of the scene. [HD/widescreen version]. (00:13:25)
The One Where Heckles Dies - S2-E3
Visible crew/equipment: Right before Monica breaks the seashell lamp there's a shot of Rachel walking into her bedroom, and just as she walks through the doorway set equipment can be seen at the right side of the screen. (Viewed on widescreen).
The One Where Rachel Finds Out - S1-E24
Visible crew/equipment: When Rachel leaves the apartment to catch Ross before his flight, just as she opens the door a crewmember's sleeve and equipment are visible at the left side of the screen.
The One with the Evil Orthodontist - S1-E20
Visible crew/equipment: While Chandler's sitting at the table waiting for the phone to ring, Joey rushes into the apartment because of telescope guy, and when Rachel walks out of her bedroom the reflection of studio lighting rigs can be seen at the top of Monica's TV screen.
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel and Ross are in the apartment with Marcel, who's still wearing the pink tutu, the bottle of wine can be seen on the side table beside the teapot, but when Ross remembers the wine it's now between the teapot and the couch.
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Monica takes the newsletter from Rachel it's open to the pages with engagement news, and we can see the left page has pictures as Monica reads Mindy and Barry's notice on the right page, but when Monica wiggles out of her comment about Mindy being pretty that left page is now only words at the bottom, even though she's still open to the same page with Mindy and Barry's notice.
The One with George Stephanopoulos - S1-E4
Visible crew/equipment: At the end, while Rachel's on the phone talking about the Visa card, in the shots facing Monica, Phoebe, Joey, and Chandler when they're playing Twister, the end of the set wall can be seen at the right side of the screen. (00:15:10)
Other mistake: The photo in Rachel's passport at the airport is not of her. (00:29:45)
The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Joey walks into Central Perk and everyone's laughing about the VD ads, just as Phoebe comments that laughing can be "infectious" we can see the camera at the right side of the screen.
The One With Rachel's Assistant - S7-E4
Visible crew/equipment: After Monica tells Chandler the secret about Nancy from Phoebe's old massage place getting fired, when it cuts to the wideshot of the apartment while Rachel's standing by the fridge, we can see the camera at the left side of the screen.
The One In Massapequa - S8-E18
Visible crew/equipment: After the anniversary party, when Rachel and Ross are back at the apartment and Ross tells her that it was the easiest four hundred bucks he ever made, Rachel gets up and just as she walks around the couch we can see the reflection of the cameraman/crew member in the mirror on the wall, at the right side of the screen.
The One Where Rachel Tells... - S8-E3
Visible crew/equipment: When Phoebe asks Treeger not to mention the incident with the door to Monica and Chandler, just as Treeger uses the measuring tape we can see the opening in the wall beside the door.
The One With the Baby on the Bus - S2-E6
Visible crew/equipment: While Phoebe's outside Central Perk singing loudly Rachel introduces Stephanie, and just as the audience claps a camera can be seen at the right side of the screen.
The One After Joey And Rachel Kiss - S10-E1
Visible crew/equipment: After Monica whips her hair around and smacks herself in the face with all the shells in her hair, it cuts to Ross at his apartment, and the end of the set wall can be seen at the right side of the screen, with the sound stage visible. (00:21:45)
The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: In Joey and Chandler's apartment, when Joey is with talking to the stripper about the duck and chicken, the edge of the set is visible where Joey's bedroom is supposed to be. The wall stops short after only a couple feet [widescreen version]. (00:09:00)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross says he could escape from any uterus, Joey is holding two small books. In the next shot they have vanished and he is holding a large book. (00:02:10)
The One With The Bullies - S2-E21
Continuity mistake: When Phoebe calls by the house with the dog, a woman with a handbag is visible in the background, going into her house. About ten seconds later we see the same woman with the handbag walk towards her house again. (00:15:40)
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