The One Where Monica Sings - S9-E13
Visible crew/equipment: When Gavin goes to the door to bring Rachel soup you can see a camera man's microphone in the top of the screen. (00:10:50)
The One With Princess Consuela - S10-E14
Visible crew/equipment: At the very start when Monica mentions swinging, all the stage lights are visible in her glass of red wine. (00:00:20)
The One With the Pediatrician - S9-E3
Visible crew/equipment: When we first see Joey and Mike at the restaurant we can briefly see a boom mic above them. (00:08:25)
The One With The Vows - S7-E21
Visible crew/equipment: When Monica and Chandler are in the coffee house after they've finished their vows, there is a microphone and another piece of equipment moving outside behind Chandler. (00:19:40)
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: Just after the credits, before we see a close up of Ross, a boom mic appears at the top of the screen in the centre of the window on the right. (00:01:30)
The One With Rachel's Date - S8-E5
Visible crew/equipment: When Phoebe is telling Monica about Tim, there is someone in the background with a black mug that is reflecting some of the stage lights. (00:05:20)
The One Where Eddie Moves In - S2-E17
Visible crew/equipment: In the scene where Monica, Joey, and Phoebe are sat on the couch in the coffee house, (whilst the camera is drifting left) a boom mic at the top of the screen is visible for a short period of time. During this time the mic can be seen moving. (00:06:50)
The One With The Lottery - S9-E18
Visible crew/equipment: At the start when they have the tickets and the empty bowl, you can see some of the stage lights in the bowl's reflection. (00:02:00)
The One with the Ick Factor - S1-E22
Visible crew/equipment: When Rachel is telling everybody about the dream she had with her, Chandler and Joey in it, Ross stands up and starts talking. When he does, the stage lights are visible in the TV. (00:13:40)
The One With Rachel's Crush - S4-E13
Visible crew/equipment: When Rachel comes in at the start of the episode a stage light is reflected in the TV. (00:02:05)
The One With The Ball - S5-E21
Visible crew/equipment: A stage light can be seen above Ross when he asks Rachel how much she paid for her cat. (00:04:05)
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: In Central Perk when Ross realises he's going to be a father, a black and white boom mic can be seen at the top of the screen. (00:16:50)
The One With Princess Consuela - S10-E14
Visible crew/equipment: When Rachel announces a job in Paris, a stage light is reflected in the pot behind her. (00:20:45)
The One With The Ball - S5-E21
Visible crew/equipment: A cameraman can be seen in the TV when Rachel is on about the cat she had as a kid. (00:04:25)
The One With The Inappropriate Sister - S5-E10
Visible crew/equipment: When Ross and Monica are wrestling, the stagelights can be seen in the tv. (00:12:45)
The One With Ross's Grant - S10-E6
Visible crew/equipment: When Joey turns the video off, the end of the set is visible in the TV. (00:15:10)
The One With The Dirty Girl - S4-E6
Visible crew/equipment: When Monica leaves the kitchen into the next scene, the boom mic is visible at the top of the screen above the kitchen door for a short period of time. (00:07:40)
The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: After Phoebe gets very annoyed by the leather pants gift, when she stands up and walks to the bathroom the boom mic can be seen at the top of the screen, just as she pulls the crepe streamer down.
The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: After Phoebe looks down at her belly and scolds the triplets for kicking one another, when Joey walks in and asks if he can borrow a big bowl, studio lighting rigs can be seen at the top right side of the screen.
The One With Chandler In A Box - S4-E8
Visible crew/equipment: When Monica and Tim are on the balcony, we can see the end of the set wall, as well as studio equipment and lighting, at the 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.