The One with the Monkey - S1-E10
Visible crew/equipment: When Joey the Elf deliberately jingles his elf shoes, Chandler's head may explode because of all the unspoken mocking jokes. It then cuts to a shot of Marcel, and the trainer's hand is visible in the bottom left corner of the screen. (00:07:25)
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: When Phoebe knocks on Joey's door you can just see 2 orange T markers on the floor. (00:22:10)
The One with the Sonogram at the End - S1-E2
Visible crew/equipment: Ross stands up to tell his parents about what has happened with Carol. When he does he walks round the table and stands under a very visible boom microphone. (00:12:05)
The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Joey walks into Central Perk after the VD poster montage, a tape marker is visible on the floor behind Chandlers spot on the sofa. (00:10:40)
The One with the Thumb - S1-E3
Visible crew/equipment: At the end, just as Monica walks off a tape marker can be seen on the floor where she was stood. This is as the credits are on screen. (00:22:30)
The One with the Monkey - S1-E10
Visible crew/equipment: After Max tells Phoebe that he and David got the grant and are leaving for Minsk on January 1st, when Phoebe goes to see David, just as she knocks on the door a boom mic can be seen moving at the top of the screen, before it cuts to David's closeup. (00:12:15)
The One with the Boobies - S1-E13
Visible crew/equipment: When Joey's mum pushes the sofa bed away, a crew member can be seen hiding behind the sofa. (00:17:00)
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Joey and Chandler walk into their apartment and the table falls over when Joey puts the key on it, the edge of the set and studio lighting are visible at the top of shot. The end of the set wall is also visible at the right side of shot. (00:04:50)
The One with the Monkey - S1-E10
Visible crew/equipment: When Chandler is demanding someone to kiss him, a boom mic can be seen slightly dropping into the shot. (00:24:20)
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.