The One Where Rachel Has a Baby, part 1 - S8-E23
Continuity mistake: At the beginning, when Rachel first arrives at the hospital, she is talking about the hospital not being out of rooms. She points to herself with her right hand saying 'What if I was the president?' Then when the shot changes to include Ross she is pointing to herself with her left hand, then it cuts back to just Rachel and she is using her right hand again. (00:01:25)
The One Where Rachel Has a Baby, part 1 - S8-E23
Continuity mistake: When the couple who has bad pet names for each other is sharing the maternity room with Rachel, the man is unpacking a suitcase that he closes, but in the next shot its open and he flips the top closed again. (00:09:10)
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.