The One Where They All Turn Thirty - S7-E14
Continuity mistake: Rachel is said to be the youngest in the group as they reminisce about their 30th birthdays, however this episode reveals that almost all of the characters ages have been inconsistent throughout the series. In Season 1, Joey is said to be 25. In Season 2, he says he is 28. In S7 E1, he says he is 31. In Season 1, Monica is said to be 26. In Season 7, she should therefore be at least 32. Rachel graduated high school with Monica, so she should also be about 32 in S7, not just turning 30. She would have been 26 in S1. But, in Season 4, she refers to herself as a "28-year-old cheerleader". Based on Season 1, Joey should actually be the youngest member of the group, not Rachel.
The One Where They All Turn Thirty - S7-E14
Continuity mistake: Rachel's birthday has always been in May, not February/March. (00:16:00)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In one of Monica's flashbacks, her hands move between shots with no time to do so. (00:10:50)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In the shot of Tag giving Rachel a scooter, her shirt is fine. The next shot of Rachel, she has a bow from the present on her shirt. The next shot is of Chandler, then next shot of Rachel the bow is gone again. (00:11:55 - 00:12:25)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: When Monica is at the party and she is drunk, there is one point when she is sitting down on a chair with Chandler on her right. Chandler is holding her left hand (which has a snack in it), but when it cuts to a front view of Monica, suddenly both her hands are on her lap. (00:13:45)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: As Monica is giving her speech while drunk, at one point her hands go from her sides to gripping each other between shots. (00:00:10)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In The One Where They All Turn Thirty, it is Rachel's birthday. They show flashbacks of all the other Friends' thirtieth birthdays despite Monica's birthday supposedly being months after Rachel's. Plus, earlier on in the show Joey was 25 when Monica was 26, and since Monica and Rachel were in the same grade Joey should actually be a year younger than them, not a year older.
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.