The One With Joey's New Brain - S7-E15
Visible crew/equipment: When Monica and Chandler are going over to the window to see Ross playing the bagpipes, the head of a crew member is visible on the left side of the screen, standing by the framed poster. (00:07:30)
The One with the Candy Hearts - S1-E14
Visible crew/equipment: Just as Joey and his date are leaving, a stage light and the top of the set drop into view above Chandler. (00:08:10)
The One with the East German Laundry Detergent - S1-E5
Visible crew/equipment: When the horrible woman enters, a tape marker is visible on the floor by the machines. (00:11:20)
The One Where Monica Gets a Roommate - S1-E1
Visible crew/equipment: We get a close-up of the coffee pot when Rachel asks if anyone would like some. In this shot, there are 3 stage lights reflected clear as day. (00:27:50)
The One Where Monica Sings - S9-E13
Visible crew/equipment: After Joey dips his finger into the hot wax and smears it all over his hands, when Sonya walks out of the back room we can see her tape mark on the floor, which she promptly steps on.
The One After the Superbowl, part 2 - S2-E13
Visible crew/equipment: When Joey walks into the bathroom and starts whistling, the shadows of the camera and a passing crew member can be seen on the door of Chandler's cubicle, then the camera's shadow moves as Joey walks toward Chandler and also when Joey's about to stand on the toilet.
The One Where Ross Hugs Rachel - S6-E2
Visible crew/equipment: After Ross tells Phoebe that he does not have feelings for Rachel, just as Ross walks into the apartment to find Rachel crying, the shadow of the moving boom mic can be seen on the wall at the top, left side of the screen. (00:20:15)
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: While Ross is trying to fix the position of the cavemen in the museum, a boom mic can be seen above his head.
The One Where Nana Dies Twice - S1-E8
Visible crew/equipment: When the scene cuts from Joey and Mr. Geller watching the game, to several people watching the game, a boom mic is visible at the top of the screen and the camera tilts slightly. (00:19:00)
The One With All The Candy - S7-E9
Visible crew/equipment: After Ross gives Phoebe the bike and she is leaving to ride it for the first time, the stage lights are visible in the rear view mirror.
The One With Ross's Library Book - S7-E7
Visible crew/equipment: When Ross says, "I work here," there is a stage light at the top to the right of Ross's head. (dvd)
The One Where The Stripper Cries - S10-E11
Visible crew/equipment: In the scene with the conversation with the stripper, there is a large vase on the kitchen table. Several lights, the top of the stage and a few crew members are reflected in it.
The One With Joey's Bag - S5-E13
Visible crew/equipment: When Joey walks into Monica and Rachel's apartment to tell the gang he didn't get the part thanks to the bag, as he approaches the couch you can see the end of the stage over Joey's right shoulder. (00:21:15)
The One In Barbados, part 2 - S9-E24
Visible crew/equipment: Right before Ross' speech begins, as the camera pans down, if you look at the top of the screen, you would be able to see the top of the set and a set light. (00:31:20)
The One With Phoebe's Cookies - S7-E3
Visible crew/equipment: When Ross asks what do with all the cookies, a boom mic can be seen at the top of the frame. (Full-screen version only).
The One With Princess Consuela - S10-E14
Visible crew/equipment: When Ross enters Central Perk with champagne, straight away when he walks over to the sofa, look above the door. In the reflection of the top window, you can see several stage lights. (00:08:45)
The One With Ross's Tan - S10-E3
Visible crew/equipment: When Rachel is talking to Monica about how weird the thing with Joey was, behind her in a yellow vase, you can see a huge light blur reflected from a stage light. (00:12:50)
The One With Chandler In A Box - S4-E8
Visible crew/equipment: When Chandler is climbing out of the box, you can see the bottom of the set spotlight right above the bathroom door. (00:20:35)
The One With Rachel's Other Sister - S9-E8
Visible crew/equipment: When Amy says, "Stupid Thanksgiving," a boom mic can be seen above Rachel's head.
The One With The Truth About London - S7-E16
Visible crew/equipment: As Joey is entering Monica and Chandler's apartment, there is a black microphone visible for a few seconds moving above Joey's head as he is walking towards Monica and Chandler at the table.
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.