The One Where Ross Can't Flirt - S5-E19
Other mistake: While everyone's watching Law and Order for Joey's big scene, Rachel, Phoebe, Monica, and Chandler are sitting on the couch and Ross is standing behind them, but in the TV's closeup the screen reflection reveals an empty couch.
The One Where Ross Can't Flirt - S5-E19
Continuity mistake: After Joey runs out of the apartment to go make the fake videotape, when it cuts to Rachel walking back into the apartment the table with the tablecloth is quite far away from the front door, but when Caitlin knocks and Ross rushes to go flirt with her that table is near the door. (00:13:35 - 00:15:15)
The One Where Ross Can't Flirt - S5-E19
Continuity mistake: When Phoebe asks Rachel for the earrings she borrowed, Chandler is visible in the background, standing up with one leg on the table and talking to Joey. When the camera angle switches, Chandler is sitting down. (00:05:00)
The One Where Ross Can't Flirt - S5-E19
Continuity mistake: When Ross first tries to flirt with the pizza girl he has money in his hand. When Chandler walks over he gives his own money for the pizza, she leaves, and Ross still has his money. In the next shot when he shuts the door, his hands are empty, then it is back in the next shot when Ross yells at Chandler.
The One Where Ross Can't Flirt - S5-E19
Continuity mistake: In the scene where the gang is watching Joey's "substitution" video, you can easily see the reflection on the television that no one is sitting on the couch, but when the camera goes back to the gang, they're sitting down on the couch. (00:19:30)
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.