Other mistake: The photo in Rachel's passport at the airport is not of her. (00:29:45)
Other mistake: When Phoebe and Ross are at JFK, some of the people who are at that airport are the same people who are also at Newark. It's particularly funny to see the people behind Ross and Phoebe at JFK when Phoebe claims they're on their honeymoon, and when it cuts to Rachel at Newark as she's looking for her boarding pass, those same people are there too.
Other mistake: When Joey sat in the paint the first time, there was a mark, but the second time, it didn't leave a mark.
Other mistake: When Rachel attempts to board the plane the first time, the man at the desk looks at her passport upside down.
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.