The One Where the Monkey Gets Away - S1-E19
Visible crew/equipment: When everyone walks in while Ross and Rachel are talking, just as Joey says that he doesn't need violence to enjoy a movie, in the small mirror behind Joey we can see the reflection of equipment moving, presumably a reflector screen.
The One with the Evil Orthodontist - S1-E20
Visible crew/equipment: While Chandler's sitting at the table waiting for the phone to ring, Joey rushes into the apartment because of telescope guy, and when Rachel walks out of her bedroom the reflection of studio lighting rigs can be seen at the top of Monica's TV screen.
The One with the Fake Monica - S1-E21
Visible crew/equipment: While they're all looking at Monica's credit card statements, when Ross tells Marcel to stop humping the lamp and also when Marcel runs off to Rachel's bedroom, the reflection of the ceiling's studio lighting rigs can be seen on the TV screen.
The One with the Fake Monica - S1-E21
Visible crew/equipment: After Marcel has humped the chair, when it cuts to Joey walking in saying that there already is a Joseph Stalin, we can see the reflection of a crew member (presumably female) in the small mirror on the wall who's wearing a black top-and it's not Rachel, the angle is off.
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 the Ick Factor - S1-E22
Visible crew/equipment: In the scene when Rachel is sleeping next to Ross, you can see part of the mattress behind the sofa which cushions his fall later on when he trips. (00:20:40 - 00:22:55)
The One with the Ick Factor - S1-E22
Visible crew/equipment: After Ethan and Monica talk about "at gunpoint" being a place, when Monica asks Ethan to stay over it cuts to a shot facing Ethan and we can see that the back wall is less than half a wall.
The One Where Rachel Finds Out - S1-E24
Visible crew/equipment: When Rachel is on the balcony with her date, after she kisses Ross and says, "Wow!", the shot changes back to her date. While he is saying, "Exactly" you can see a camera man on the left side of the screen. Then when the shot changes to show Rachel and her date you can see him move out of the shot. (00:19:45)
The One Where Rachel Finds Out - S1-E24
Visible crew/equipment: After Monica asks Rachel if there's someone else and shouts, "Why the hell are you dumping my brother?," when it cuts to Chandler sitting at the counter, the edge of the set can be seen at the left side of the screen, and also note the front door is wide open for the camera access. Additionally, when Joey joins Chandler at the counter the juice box has black tape covering its brand name.
The One Where Rachel Finds Out - S1-E24
Visible crew/equipment: When Rachel leaves the apartment to catch Ross before his flight, just as she opens the door a crew member's sleeve and equipment are visible at the left side of the screen.
The One With Ross' New Girlfriend - S2-E1
Visible crew/equipment: When Rachel's at the airport and freaks out after seeing Ross with Julie, right before she steps up on the chair the grey crash mat can be seen on the floor, behind the man who's wearing white pants and is seated.
The One With the Breast Milk - S2-E2
Visible crew/equipment: In the first part of the episode, there is no ceiling above the secret closet, revealing a whole lot of stage lights. (00:01:20)
The One Where Heckles Dies - S2-E3
Visible crew/equipment: When Mr. Heckles is being taken away, just as the officer starts to follow the gurney the shadow of the moving boom mic can be seen on the wall behind him, at the right side of the screen. (Widescreen version).
The One Where Heckles Dies - S2-E3
Visible crew/equipment: Right before Monica breaks the seashell lamp there's a shot of Rachel walking into her bedroom, and just as she walks through the doorway set equipment can be seen at the right side of the screen. (Viewed on widescreen).
The One Where Heckles Dies - S2-E3
Visible crew/equipment: After Mr. Heckles is taken away, when it cuts to Phoebe walking out of the kitchen, the reflection of studio lighting array can be seen on the TV screen. Also later in Heckles' apartment, studio lighting's reflected on his TV screen.
The One Where Heckles Dies - S2-E3
Visible crew/equipment: After Monica yells "Stop with the broom, we're not making noise," when both Monica and Rachel stomp their feet the studio lighting can be seen at the top of the screen, over Ross (this doesn't refer to Monica's star light fixture). And when the others join in stomping their feet, we can also see the boom mic dip into view.
The One With Phoebe's Husband - S2-E4
Visible crew/equipment: After the opening credits, just as Joey says that it's unbelievable Phoebe can be married, a camera and yellow electrical cord can be seen at the left side of the screen, and a bit of it is still visible in following shots when Monica mentions the cheeseburger.
The One With Five Steaks and an Eggplant - S2-E5
Visible crew/equipment: In the part where Ross is on the phone with Julie he says "Say hi to Julie in New Mexico." When everyone is shouting "Hi Julie" look above their heads and you will see a boom mic dip into the shot. (00:03:10)
The One With the Baby on the Bus - S2-E6
Visible crew/equipment: While Phoebe's outside Central Perk singing loudly Rachel introduces Stephanie, and just as the audience claps a camera can be seen at the right side of the screen.
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)
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.