The One Where Chandler Gets Caught - S10-E10
Continuity mistake: Ross claims he looks into Monica and Chandler's and watches them eating dinner and watching TV. His apartment is a floor lower down than theirs and with the balcony wall, the sofa and tables distance from the window and the fact the bottom of the window is higher than the floor, there is no way Ross would be able to see that far in. We have seen in the past that he can basically only see who is at the window. (00:19:05)
The One With Joey's Porsche - S6-E5
Visible crew/equipment: Anytime we see the Porsche, there is always a stage light above it. (00:03:30)
Continuity mistake: When Ross says , "Yes, I am." after Mona calls him sweet, His hands are by his side. Next shot one of them is by his chest. (00:16:30)
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: In the bar, Kathy is trying to set Chandler up with one of her friends. When the camera is facing Chandler, we see Kathy's hand rubbing Joey's back, but when it cuts to a front shot of Joey and Kathy, her arm is down in front of her. Then without having had enough time to move, her elbow is up on the table and she is holding hands with Joey. (00:16:10)
The One with the Fake Monica - S1-E21
Revealing mistake: In the scene when Marcel has to get on the plane. It is obvious that David Schwimmer is just shaking his leg and Marcel is doing nothing besides sit on David's foot. It is especially obvious in the second shot. (00:20:45)
The One Where Joey Dates Rachel - S8-E12
Continuity mistake: At the end Ross rips the map but in the next shot it's repaired. (00:21:00)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: In the scene where Monica and Ross discuss how Emily has decided to call off the wedding after Monica suggests they postpone the wedding, Monica is wearing a black watch on her left wrist. This disappears and re-appears a number of times throughout the scene. (00:15:00)
The One Where Rachel Tells... - S8-E3
Continuity mistake: In the scene where Monica and Chandler are trying to get in the first class lounge, Monica has a green bag on her left shoulder. It switches mid-scene to her right hand, and then appears back on her left shoulder. (00:08:40)
The One With The Blind Dates - S9-E14
Continuity mistake: At the end of the blind date, in shots of Rachel, her date Steve is holding her hand with both of his, but from the reverse angle he's only using one. (00:18:45)
The One With The Giant Poking Device - S3-E8
Revealing mistake: The giant poking device is supposedly long enough to reach right across to the next building, but after they wake up Ugly Naked Guy, Joey says "retract the device!" and after pulling back about a foot of it the end suddenly pops up at the bottom of the screen. (00:20:25)
The One With The Truth About London - S7-E16
Continuity mistake: When Rachel goes to Carol's house and tries to tell Ben to stop playing pranks, her bag changes from being on her shoulder to in her hand in almost every shot. (00:12:25)
The One With All The Haste - S4-E19
Continuity mistake: Phoebe comes in wearing Santa pants. When Joey and Chandler point this out, Chandler's legs are crossed or uncrossed, depending on the camera angle. (00:04:10)
The One With the Baby on the Bus - S2-E6
Continuity mistake: When Stephanie is singing "Angel in the Morning", there is a person in overalls sitting behind the green pole. The shot changes to Phoebe outside and you can still see the person; it changes back to Stephanie and the person is now sitting on the next table. (00:16:00)
The One With The Truth About London - S7-E16
Other mistake: Right at the very end, when Joey is in the fat-suit and picks up a piece of food and says "How you doin'?" he doesn't put it in his mouth, he just lifts it to his lips, stops, and tries to stay still. If this had been a freeze on the part of the director then fair enough, but it isn't as he and particularly Monica are still moving. It just looks rather corny and amateur, as though they are waiting for the "cut" to be called. (00:28:00)
The One After Ross Says Rachel - S5-E1
Audio problem: Monica tells Ross that he should keep looking for Emily, and Chandler says "Yeah, for about 30 minutes." But the audio doesn't match up with his lip movements, indicating this line was dubbed. (00:10:26)
The One With Phoebe's Dad - S2-E9
Visible crew/equipment: Outside the coffee shop, Phoebe pulls up in her grandmother's taxi dragging what appears to be a sound equipment cable. (00:10:00)
The One Where Ross Is Fine - S10-E2
Audio problem: When Ross is drunk and talking to Rachel, Joey and Charlie on the couch in his apartment; he begins to say "Where do you think we can go?" but his mouth does not move. (00:12:10)
The One with George Stephanopoulos - S1-E4
Visible crew/equipment: When Monica climbs out the window with the pitcher of Tiki Death Punch while Rachel and Phoebe are on the balcony, we can see the end of the set wall inside and a crew member moving around back there.
The One With All The Wedding Dresses - S4-E20
Visible crew/equipment: After Ross announces that he and Emily will be getting married in a month, there's a shot of Joey and Chandler, and when it cuts back to Ross saying, "Yup!" the reflection of the boom mic can be seen on the framed picture hanging on the bathroom door.
The One With The 'Cuffs - S4-E3
Continuity mistake: The handcuffs that Joanna uses on Chandler have a single metal bar connected via pivot to a double bar with the lock area. When Joanna first cuffs Chandler, the double bars on both sides face up at his wrists, but when Chandler's on the phone and when Rachel unlocks his right cuff, the handcuffs are going round his wrist the opposite way with the single bars facing up - quite impossible. Then the same thing occurs when Rachel handcuffs Chandler to the filing cabinet.
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.