The One With The Chicken Pox - S2-E23
Factual error: The symptoms (spots, fever, etc) of chicken pox only develop 2 - 3 weeks after exposure to the virus. Therefore, when Ross knew that Ben had chicken pox, Phoebe shouldn't have developed the condition until at least two weeks later, and Ryan certainly shouldn't have developed the disease until the end of his stay (as Phoebe was his only contact with the virus). (00:09:30)
The One With The Chicken Pox - S2-E23
Continuity mistake: When Phoebe and Ryan are playing Monopoly, she rolls the dice and one goes off the board (but stays on the table). It then cuts to a wider view of them and both dice are back on the board. (00:09:50)
The One With The Chicken Pox - S2-E23
Continuity mistake: When Monica says about Richard not having a 'thing', her arms change place depending on the shot. (00:14:10)
The One With The Chicken Pox - S2-E23
Factual error: Ryan is a LCDR submariner, who had been on a sub deployment for the last two years. but at no time does he wear his dolphins pin. A true submariner would sooner forget his skivvies than his pin.
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.