The One With The Hypnosis Tape - S3-E18
Factual error: When Pete takes Monica to Rome for the date this would have been impossible as Rome is 6 hours ahead of New York and at least 4/5 hours travel time, assuming they went by Concorde (double that otherwise). They would have had to have left New York early in the morning to make dinner for 8/9 pm in Rome.
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.