Continuity mistake: In this episode, they say the reason Kip was phased out was because he dated Monica and they broke up badly. However, in the first season (in the "Dozen Lasagnes" episode) Chandler says Kip left because he got married. (00:13:50)
Continuity mistake: Ross, Joey and Chandler are in Chandler and Joey's appartment talking about Ross' decision. Chandler has a green bottle in his hand. He puts it down behind the computer by the microwave, but when Ross starts listing Rachel's "cons" the bottle's suddenly at the opposite end of the counter. (00:07:40 - 00:08:25)
The One with the Stoned Guy - S1-E15
Continuity mistake: When the stoned guy says they should make macaroni and cheese, Monica holds out her hands. In the next shot, her hands are clasped together. (00:18:50)
The One With The Video Tape - S8-E4
Continuity mistake: As Joey says thanks to Ross for his offer to help him if he has a problem with the ladies, he puts his hand on Ross's arm. Camera cuts and it is by his side with no time to move it. (00:11:35)
The One Where Rachel Tells... - S8-E3
Continuity mistake: When Joey finds out condoms are only 97% effective, he has his arms crossed. The camera changes angle and he now has them by his side. (00:14:30)
Continuity mistake: When Rachel spits out the champagne for the first time, her necklace is center chest. When the camera cuts it is far right. (00:13:25)
The One With The Halloween Party - S8-E6
Continuity mistake: The amount of carrot Chandler has keeps changing from less to more. (00:10:35)
The One With Monica and Chandler's Wedding, Part 1 - S7-E23
Continuity mistake: When Monica is talking to Chandler about nothing having gone wrong, Chandler's arms are crossed. The camera cuts, and his arms are down by his side. (00:06:50)
Continuity mistake: When Rachel is talking to Phoebe about cremating the coat there is a mirror behind her with a laptop reflected in it. The reflection shows it switched on, but in the wider shots it is switched off. (00:09:15)
The One Where Ross Dates a Student - S6-E18
Continuity mistake: When Chandler, Joey and Ross are talking about Donna Keystone from college, Ross is holding a water bottle; it disappears, then he is holding it again. (00:13:15)
The One with the Monkey - S1-E10
Continuity mistake: When Rachel says about her 6th date with Paulo, she is holding a decoration for the tree. In the next shot the decoration changes to a much larger object. Then, in the next shot, as she hands it to Monica, it has turned back to the original shape. (00:05:40)
The One With The Mugging - S9-E15
Continuity mistake: At the beginning when Joey is in Monica's apartment eating bacon, you see Joey reach for the bacon from the front, then in the next shot (side on) you see Joey reach for the bacon again. (00:02:10)
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: At the end of this episode when Rachel falls off the balcony, when we are looking out from Mr. Heckles' apartment, a boom mic is visible at the top of the screen just above him. (00:21:30)
The One with the Blackout - S1-E7
Revealing mistake: When Phoebe says something like, "Look, the last candle is about to go out", she starts counting down, saying "-47,-48..." and you can see Monica looking at the candle. But there is a light source behind her (it can't be a candle because she is looking at the last candle). (00:20:05)
Visible crew/equipment: When Bonnie first arrives at the beach house, when she enters the door look at the top of the screen above the left door and you will see a microphone dip into the shot for a second before the camera changes. (00:10:55)
The One Where Joey Speaks French - S10-E13
Visible crew/equipment: When Joey is calling Phoebe after she walked out of his apartment, the shadow of a camera can be seen on Monica's door. (00:08:05)
The One With The Mugging - S9-E15
Continuity mistake: In The One With The Mugging, Phoebe brings her 'crap from the street' box to the coffee shop to show Ross, and she opens the flaps of the box twice. (00:19:15)
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 With The Ultimate Fighting Champion - S3-E24
Continuity mistake: In the scene with Robin Williams and Billy Crystal, there is a shot of Rachel, and her hair is hanging straight down. The next shot of Rachel is from a different angle and there is a section of hair behind her ear; in the shot after that it is hanging straight again, and is then behind her ears again. (00:00:40)
The One with the Thumb - S1-E3
Continuity mistake: When Phoebe sees Lizzie, she is sat near her trolley feeding pigeons which are out of shot. In the next shot two pigeons have appeared next to the trolley. (00:11:40)
Answer: Usually by the seventh night of Hanukkah you don't know what to get the other person, and you will probably resort to getting the other person something insignificant. Chandler is basically saying that the pen is a stupid gift.