The One With The Lesbian Wedding - S2-E11
Trivia: Rachel says about her mother who thinks about a divorce and wants to be like her daughter : "Well, couldn't she have just copied my haircut?" A little reference to the fact that the Rachel haircut was one of the most copied one at the time. (00:10:15)
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.