The One With The Ball - S5-E21
Other mistake: The guys start the ball-throwing game at around 2 in the afternoon. Later, they mention that it's been going for 10 hours, making it around midnight. Why would Rachel, who never cooks, be defrosting a chicken? And why would she be doing so at midnight?
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.