When he is obsessing over October 20th because it's the first time he had sex with Carol, Monica said, "I was hoping you wouldn't remember." In the next episode, Joey and Monica are on a date with Angela and Bob and Angela tells Monica that Bob is terrific in bed. Her response: "Wow. My brother never even told me when he lost his virginity." So, that's false.
According to the flashback episode, Ross found out that Carol was a lesbian a year before the pilot episode took place (Rachel says in the episode, "In one year from today I'll be Mrs. Barry Farber"), but in the pilot he is just now learning she was a lesbian or it took her an entire year to move out, which is weird because she would have still been having sex with Ross after he found out because she's pregnant a year later.
Although it's since been fixed in the Netflix version and on TV, in the one where Chandler freaks out Janice, the ice cream container he eats when he's sad changes colors … many times from purple to green and back again.
10. Hugo Boss Died in 1948
Why doesn't the man who works for Gucci know this?
Phoebe gets all bent out of shape in season 8 because Monica has never let Phoebe massage her. Except that in season 7, she says "It's already February and I've only given two massages, and they were both the worst tippers in the world!" To which Monica responds, "That was me and Ross."
She tries on one dress at the fancy store, grabs a totally different one at the discount store in Brooklyn and the one she tries on for Chandler telling him not to like it is a different one. So, there's that.
Joey has seven sisters. Everyone knows this, except Joey of course. In the episode where Ross kisses Mrs. Bing, Joey says, "You don't think my mom is sexy? I'll have you know that Gloria Tribbiani was a handsome woman in her day, alright? You think it's easy giving birth to seven children?" Okay Joey, except she gave birth to 8 people.
Or not … because he eats ice cream with Marcel and Elizabeth.
18. The Velveteen Rabbit
Since when is The Velveteen Rabbit Chandler's favorite book? In season 8 Monica gets him the bunny costume because that was his favorite children's book. You know who else loved the Velveteen Rabbit? Kathy. You think he would have mentioned that to her?
Janice is stood up by a boyfriend when she has dinner with Monica and Chandler before the wedding, but she has a baby on the same day that Ross and Rachel have their baby, saying that she nabbed Sid a year ago at the dermatologist's office. That timeline is completely off for her to meet Sid, get pregnant and have the baby on the same day.
20. Phoebe's Italian Skills
She never understood Paolo in season 1, but then when Joey's grandma comes in season 5 she speaks perfect Italian to her.