The One Where They All Turn Thirty
Rachel frets over turning 30, prompting everyone else to remember what they did when they reached the same milestone. After realizing that Tag is too young and immature, she breaks up with him.
Note: In episode 3.10 “The One Where Rachel Quits”, set in December 1996, Chandler says Rachel is 28 and so she should turn 33 in this episode, set in early 2001. Moreover, it is previously said (elsewhere in seasons 4 and 5) that Rachel was born on May 5th and not in the wintertime.