The One With Five Steaks and an Eggplant - S2-E5
Continuity mistake: When Chandler picks up the phone, he says "Bob here" and Ross is sitting by the bar on the living room side. When the scene starts again after the credits, Ross is getting a drink out of the refrigerator. (00:01:00)
The One With Five Steaks and an Eggplant - S2-E5
Continuity mistake: When Ross is giving his toast to Monica, when he's finished he drinks from his glass. Later when Chandler arrives, it is still at the same level. (00:07:10)
The One With Five Steaks and an Eggplant - S2-E5
Visible crew/equipment: In the part where Ross is on the phone with Julie he says "Say hi to Julie in New Mexico." When everyone is shouting "Hi Julie" look above their heads and you will see a boom mic dip into the shot. (00:03:10)
The One With Five Steaks and an Eggplant - S2-E5
Plot hole: Chandler has always loaned Joey money for various things (rent, acting classes, Christmas gifts, etc), so he shouldn't be surprised to learn that Joey doesn't have money for fancy dinners or birthday celebrations. Plus, Joey never seems to have a problem taking money/handouts from Chandler - why now? Also, Chandler explains that they're buying Ross a cake ($20), but why doesn't Monica (the chef and his sister) just make him one? (00:07:50)
The One With Five Steaks and an Eggplant - S2-E5
Continuity mistake: When Chandler is seducing Jade in Central Perk, he turns to face Ross after handing her the tissues. The camera then cuts to another angle where he is still facing Jade, and then he turns again to face Ross. (00:06:40)
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.