Joey was originally written as a jerk. When Matt LeBlanc questioned why the others would be friends with him, the character was changed.
When Courteney Cox dressed as fat Monica for the first time, Matthew Perry walked right past her without recognizing her.
Lisa Kudrow and her best friend wrote "Smelly Cat" one night when they were drunk, and it eventually got written into the show.
When Matt LeBlanc auditioned for the role of Joey, he had eleven dollars to his name. When the cast got their first paychecks, the first thing that LeBlanc bought was a hot dinner. Courteney Cox bought a car.
Courteney Cox was originally supposed to play Rachel. In Friends: The Reunion (2021), she explained that she asked to play Monica instead, since she related to her more.