The One with the Stoned Guy - S1-E15
Continuity mistake: After Chandler walks in on Ross and Joey talking dirty, Ross is holding his right hand up as he and Joey start to explain to Chandler. In the next shot his arm is by his side. (00:13:10)
The One with the Candy Hearts - S1-E14
Continuity mistake: Just before Carol and Susan enter the restaurant, Ross reaches for the menu with his left hand and his right hand is under the table. In the next shot his right hand is holding onto a cup on the table. (00:11:20)
The One with the Boobies - S1-E13
Continuity mistake: After Phoebe tells everyone she broke up with Roger, Monica has her legs crossed and Rachel has them uncrossed. In the next shot, Monica's are now uncrossed and Rachel's are crossed. (00:20:50)
The One with George Stephanopoulos - S1-E4
Continuity mistake: After Rachel speaks to her pregnant friend, they manage to swap places between shots. (00:05:50)
The One with the East German Laundry Detergent - S1-E5
Continuity mistake: At the start of the episode when Ross says, "Multiple orgasms", you can see Chandler's boot is not resting on his knee. In the next shot it has appeared from nowhere. (00:00:55)
The One with All the Poker - S1-E18
Continuity mistake: When Rachel finds out she has an interview she is holding the letter in her left hand. When the shot changes, the letter is in her right hand. (00:09:05)
The One with the Boobies - S1-E13
Continuity mistake: When Phoebe's boyfriend is talking about Chandler at the coffee shop, the cookie he is holding jumps from his left to his right hand in an instant between shots. (00:03:20)
The One with Mrs. Bing - S1-E11
Continuity mistake: In the final scene Rachel passes out copies of her draft for her book. She gives out all her copies and asks for their opinion. However, near the end of the scene after waving her arms around empty handed a copy of her script magically appears in her hands. (00:21:10 - 00:21:45)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Chandler tries to fire Nina, he holds his left hand to his face. In the next shot he is holding his right hand up. (00:10:20)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: During the song at the beginning of the episode, keep your eye on Ross's mug. He is holding it in his lap, then there is a shot of Monica with Ross's empty saucer on the table. In the next shot, the mug has appeared on the saucer. (00:00:30)
The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey asks Ross 'how could you let this happen' in the hall, his sleeves are down to his wrists. In the next shot, they are rolled up. (00:10:25)
The One with George Stephanopoulos - S1-E4
Continuity mistake: When Rachel is explaining that she's not going back home, the friend with her arm on the back of the sofa behind her has her sleeve part the way up towards her elbow leaving a very prominent gap between the sleeve and bracelet. When the camera comes back to her the gap has now gone. (00:08:20)
The One with George Stephanopoulos - S1-E4
Continuity mistake: When Rachel's friend who is pregnant appears in Central Perk, she says she's like a Duplex. When she does, her left-hand goes from outstretched to on her belly. (00:06:10)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: When Ross shows Chandler and Joey the can of "Carol's favorite beer" it's unopened as Ross makes a crack about how he "should have known," but in the next shot we see Ross lifting the can and drinking from it, even though he never actually pulled open the stay-tab between the two shots (viewed in widescreen). [In the extended version of the episode you see Ross open the can before taking a drink. In the standard version, the mistake is valid]. (00:09:55)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: Before Monica stomps on Paul's watch, the chair closest to the fridge does not have fabric backing, then when Ross eats the Oreo and walks toward his jacket the chair closest to the fridge is now fabric backed and his jacket hangs from a chair with no fabric, plus there are only four chairs around the table. However, when Ross picks up his jacket this chair is now fabric backed, the chair closest to the fridge doesn't have a fabric back yet again, and there are now five chairs around the table. (00:27:00)
The One with the Evil Orthodontist - S1-E20
Continuity mistake: When Rachel's in Barry's office her black handbag is hanging over the counter, but after Billy walks in on them and Barry pretends to look in Rachel's mouth, the bag's lying on the counter.
The One with the Evil Orthodontist - S1-E20
Continuity mistake: When Rachel walks into Central Perk she puts her black handbag down behind the couch and proceeds to talk about Barry, but after Ross smacks Chandler's arm to prompt him to speak up, the handbag's strap appears on Rachel's wrist.
The One with the Sonogram at the End - S1-E2
Continuity mistake: When Monica holds the glass pan of lasagna up over her head to try and find Rachel's ring, when it cuts to the next shot the lasagna is still in the air, but it's different - note burned corners, etc. (00:06:10)
The One with George Stephanopoulos - S1-E4
Continuity mistake: When Ross wrestles his puck away from the little kid in the emergency room, it goes flying at the receptionist. The shot cuts, and it hits her from a completely different angle.
The One with the Stoned Guy - S1-E15
Continuity mistake: When Chandler says Ross isn't speaking metaphorically, he gestures with his right hand. In the next shot, both his hands are in his pockets. (00:06:05)
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