The One With Frank Jr. - S3-E5
Continuity mistake: When Frank Jr. holds a white sheet around himself, while talking to Phoebe about how she really is a masseuse, etc., the gathered sheet in his hand keeps changing repeatedly throughout the scene. (00:14:10)
The One With Frank Jr. - S3-E5
Continuity mistake: When Phoebe is talking to Monica while Frank Jr is doing karate on the balcony, the blue cup in front of her moves, disappears and is back again. (00:10:20)
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank has the towel wrapped around him, the knot on his chest changes a lot between shots.
The One With Frank Jr. - S3-E5
Continuity mistake: In the scene where Joey and Monica discuss changing her bathroom tile, Joey moves the hamper to the middle of the doorway and when he kneels down to measure, the hamper is back against the wall. (00:06:25)
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank is trying to melt a spoon there's one shot where he holds the spoon high above the table, then the angle changes and he's pressing the spoon against the plate.
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.