The One Where They're Going To PARTY! - S4-E9
Continuity mistake: When Joanna stops Rachel from leaving work Rachel's holding her handbag and jacket, and there's still one bag hanging on the wall hook, but when Joanna mentions the "drinking binge" there are two bags hanging from the hook, then it's back to just one bag, yet when Joanna calls Sophie there's nothing on the hook and Rachel has both bags.
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.