The One With All The Rugby - S4-E15
Continuity mistake: During the rugby game, when Ross tells Phoebe and Joey that he thinks he's dying there are two hairsticks in Phoebe's bun in the shots facing her, but there's only one hairstick in her bun in the shots facing Ross.
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.