The One With The Halloween Party - S8-E6
Factual error: This show is set in October (it's a Halloween party). Rachel's stomach is completely flat, but according to the show, she got pregnant in April (It's stated several times by the characters on the show that Monica and Chandler's wedding was in May, and we learn in "The One With The Red Sweater" that she got pregnant a month before the wedding. Hence, April). However, by October she should have a six months' pregnant belly, which is no way resembles the perfectly flat belly she shows.
The One Where Joey Dates Rachel - S8-E12
Factual error: The premise of Chandler filling the high score list with dirty words is not possible for this game. Ms. Pac-Man only keeps track of a single high score, which is always displayed at the top of the screen. Unlike many other games of the era, there is no screen showing a list of additional top scores alongside initials during the attract mode, and there is not even a mechanism for entering initials within the game's code.
The One Where Joey Dates Rachel - S8-E12
Factual error: When Chandler is explaining that he played Ms. Pac Man all day, the Ms. Pac Man machine is unplugged, and then plugged back in. Immediately upon being plugged back in, we hear the Ms. Pac Man theme song being played. No version of a Ms. Pac Man stand-up arcade ever played the theme song upon powering on. Instead, it would silently go into "demo mode." The only way the stand-up arcade version of Ms. Pac Man would ever play its theme song was after two events occurred in order: 1. A coin was dropped in the slot (or a button was pressed on the inside of the unlocked coin drawer), and then 2. Someone pressed the '1 player' or '2 players' button to start the game. It is clear that neither of these things has happened in the scene by the time the music starts playing. (00:11:50)
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.