The One With Rachel's Dream - S9-E19
Continuity mistake: In the scene where Ross and Chandler are checking into the hotel, the box of maple candy Ross is holding keeps switching from the front of the box facing us to the back facing us. (00:07:20)
The One With Rachel's Dream - S9-E19
Continuity mistake: When Rachel is telling Monica about her dream at Central Perk, Phoebe enters and leaves her bag on the couch but it falls. However, in the next shot, her bag is right at her side on the couch. (00:14:40)
The One With Rachel's Dream - S9-E19
Visible crew/equipment: After Monica and Phoebe apologize to each other at Javu, when it cuts to Rachel walking into the apartment we can see part of the hole in the wall beside the bulletin board, and the light fixture above it is gone.
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.