Continuity mistake: When Chandler and Monica are in the birthing room and they have just been told they are having twins, her scarf keeps changing from sitting on her shoulder to being over her shoulder. (00:10:20)
Continuity mistake: When Chandler and Monica are at the hospital holding the twins right before they try and swap babies, there are two hospital tags around Chandler's left wrist which then disappear before re-appearing. (00:15:25)
Continuity mistake: While Mama Joey is looking for Chick Jr. and Duck Jr., the things pinned to the bulletin board beside the door have vanished when Monica and Chandler walk in, but after Monica walks out to check on the twins everything's back up on the board like it was before.
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.