The One With The Vows - S7-E21
Continuity mistake: After Monica says "Oooh can we lie in our vows?" it cuts to Rachel then back to Monica leaning on her hands, but when it goes for a close up she is holding the pen in her right hand, there isn't enough time for her to naturally pick it up. (00:03:10)
The One With The Vows - S7-E21
Visible crew/equipment: When Monica and Chandler are in the coffee house after they've finished their vows, there is a microphone and another piece of equipment moving outside behind Chandler. (00:19:40)
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.