The One Where Ross Got High - S6-E9
Visible crew/equipment: After Ross and Monica blurt out each other's secrets to their parents, when Jack says, "And we kind of figured about the porch swing," in his closeup we can see the end of the set wall, with the soundstage behind it and many tape marks on the floor.
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.
Visible crew/equipment: In the scene where Chandler is talking to Rachel and Ross about how Janice thought that he had somehow called her fat, if you watch Monica's closet in the back, you can see the shadow of someone walking past, under the door. (00:05:20)
The One With Ross's Inappropriate Song - S9-E7
Visible crew/equipment: When Monica comes home at the end, as Joey pulls her down on top of Chandler as to protect her eyes from seeing the tape, you can see a knee pad on Courteney Cox's knee, under her skirt. (00:14:20)
The One With The Bullies - S2-E21
Visible crew/equipment: When Phoebe goes to visit her father, there is a little dog outside. Phoebe gets back in the car and the dog jumps up the side of it. When he finally gets part way through the window, the top of the dog-handler's head is visible through the car window. (00:07:00)
The One With The Prom Video - S2-E14
Visible crew/equipment: During the prom video, Monica, Rachel, and Monica's date Roy are standing in the living room. When Roy leaves the room saying, "I'm gonna kick Chip's ass," the camera follows him out, but as it's turning the boom mic operator is visible. He's kneeling on the floor sliding the mic toward the girls. (00:20:45)
The One With The Routine - S6-E10
Visible crew/equipment: While Monica and Ross attempt to do the original end to their routine, instead of Monica catching Ross she jumps out of the way, and when Ross lands on the floor the corner of the crash mat can be seen. (Widescreen version).
The One with the East German Laundry Detergent - S1-E5
Visible crew/equipment: When the horrible woman enters, the boom mike is visible in the mirror at the top of the screen. (00:10:10)
The One With Rachel's Sister - S6-E13
Visible crew/equipment: After Jill comes to Monica's apartment, they are all around the table in the living room. As the camera is moving from Jill, to Monica and Chandler, who are sitting on the couch, a camera-man is visible in the kitchen behind them, complete with camera and trailing wires. (00:04:15)
The One With a Chick. And a Duck. - S3-E21
Visible crew/equipment: Monica is talking to Pete in the diner when he gets back from Japan. If you look at the floor at Monica's end of the counter at the very beginning of the scene, you can see the mat that is there to protect her when she falls over later. (00:02:35)
The One with the East German Laundry Detergent - S1-E5
Visible crew/equipment: While Chandler is trying to break up with Janice, and Phoebe comes to help, a cameraman is visible in the background (outside of Central Perk) walking from right to left. The camera cuts away from the window angle, then cuts back, showing another cameraman walking from left to right. (00:19:15)
The One With The Fertility Test - S9-E21
Visible crew/equipment: When Monica and Chandler are on the couch in the fertility clinic after Monica says "Nobody's gonna wanna watch that" the camera switches to a wider shot. When it does this the boom mic swiftly moves out of view. (00:12:20)
The One With All The Jealousy - S3-E12
Visible crew/equipment: After the barbershop quartet sing their "Ross song" to Rachel at her office, at the start of the next shot the camera can be seen at the right side of the screen, just as Ross walks out of Rachel's bedroom.
The One Where Chandler Can't Remember Which Sister - S3-E11
Visible crew/equipment: When Phoebe and everyone else hear the guy upstairs with the "pogo stick" Joey gets up to give him the "butt kicking of a lifetime," and just as Joey walks around the sofa we can see a crew member and camera, at the left side of the screen.
The One With The Fake Party - S4-E16
Visible crew/equipment: While Rachel's explaining how to play 'spin the bottle' the bottle she spins points to Gunther, and in the shot facing Gunther we can see the end of the set wall, at the right side of the screen.
The One With The Fake Party - S4-E16
Visible crew/equipment: After Ross finds out that Monica told Emily about how he used to play dress up and host make-believe tea parties, when Monica stands up we can see set lighting near the bathroom, at the top of the screen.
The One With All The Rugby - S4-E15
Visible crew/equipment: When Phoebe walks into the apartment while Ross and Joey are watching rugby on TV, the boom mic and a bit of the overhead studio lighting can be seen right before she sits down, and the boom mic can be seen again when Joey stands up after Chandler walks in with Janice.
The One with George Stephanopoulos - S1-E4
Visible crew/equipment: When Monica's looking out the window at George Stephanopoulos with the binoculars, the end of the set wall and overhead studio lighting can be seen at the left side of the screen. (00:15:20)
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: After Ross and Monica talk about Emily's dream of the perfect wedding and perfect guy (and Monica's pillowcase), when it cuts to Phoebe and Rachel at the apartment we can see a crew member (wearing a blue shirt) at the left side of the screen, before Phoebe mentions that she thought of a good flaw. (DVD).
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: When Joey, wearing the Union Jack hat, walks into the hotel room while Chandler's sitting on the bed, on the widescreen version we can see the end of the set wall at the right side of the screen. On the DVD, just as Joey walks across the room studio lighting can be seen at the top left side of the screen.
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.