The One With All The Resolutions - S5-E11
Continuity mistake: When Joey and Rachel are trying to work out if the other knows about Monica and Chandler, they sit at the table in silence. In a side shot of Joey they look at each other sneakily, and Joey has his arms by his sides. It then cuts to a head-on shot of Joey, and he's got his right arm over the back of the chair. (00:19:00)
The One With All The Resolutions - S5-E11
Continuity mistake: When Ross first enters Elizabeth's bathroom, the lotion is first in line on the shelf; next to it is something else and then the powder. Later, the powder is first in line on the shelf and the lotion has moved. (00:09:30 - 00:12:45)
The One With All The Resolutions - S5-E11
Continuity mistake: During the countdown to midnight, just as everyone says, "Happy New Year!", the camera cuts to Phoebe and Ross. In the background Joey and Rachel open their arms to hug each other; the camera cuts to just Joey and Rachel and they open their arms again. (00:01:00)
The One With All The Resolutions - S5-E11
Continuity mistake: Immediately when the opening scene starts, we hear from the crowd on the television that there is less than 60 seconds to midnight. However, 60 seconds later in the scene, the countdown still hasn't reached zero.
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.