1. Why does Chandler claim not to have cried since he was a child, despite evidence to the contrary?
Also, in Season 3, Phoebe tells a story where she made him "cry like a baby."
2. Why does Ross hate on ice cream, when he'd previously happily shared it with Marcel?
And Elizabeth, but Marcel is more important here.
3. Why does Rachel not remember Chandler in the first episode, despite them spending Thanksgiving together on multiple occasions?
And, y'know, MAKING OUT.
4. Why does Ross claim to have slept with only Carol in the early stages of the show, but it later comes out that he slept with the cleaning lady in college?
5. How come Chandler forgot how to palm money?
Richard taught him early on, in Season 2, but by Season 7, he tries to give the maître d' a tip in a restaurant, and fails.
6. Why are all the ages of the characters so inconsistent?
7. Similarly, why ARE their birthdays so inconsistent?
Another quick rundown — Rachel tells Gunther her birthday is May, but also claims to be an Aquarius (January). Ross, meanwhile, claims his birthday is Oct. 18 at the hospital after breaking his hand, but had previously told Gunther it was December.
9. Why do Monica and Ross have such different views on what they've talked about?
Ross announces he told everyone when he first slept with Carol, but the very next episode, Monica has no knowledge of it.
10. How does Joey forget what an Adam's apple is?
11. And how come he also forgets what air quotes are?
12. Why does Monica forget about the turkey on the head incident?
She claims it's her first Thanksgiving in "The One Where Underdog Gets Away," but when they later share their worst Thanksgiving, it's clear she has had a Thanksgiving before.
Because Joey has a turkey on his head. How does that slip someone's memory?
13. Why does Phoebe claim her father left before she was born, when he clearly sung her bedtime lullabies?
Since they inspired "Smelly Cat," this is actually extremely important.
14. Why does Rachel have a working key in Season 10, after Treeger had smashed the door down and changed the locks since she moved out?
In "The One With the Late Thanksgiving," the gang is able to get the door open (partially) because Rachel still has a key. But the locks were changed in the Season 8 episode when Joey and Phoebe accidentally lock the door, and claim there's a gas leak.
15. Why did Monica and Chandler break their promise to name their first child Joey?
A disgraceful betrayal.
16. How come Phoebe doesn't know the word "sous" despite being fluent in French?
She mistakes Monica's sous chef for her boss in "The One With Rachel's Date," but then teaches Joey how to speak French, and appears to be more or less fluent in it.
17. How come none of the three die-hard Die Hard fans notice the remarkable resemblence between Bruce Willis and Elizabeth's dad?
And while we're here...
"Susan Sarandon" was on Ross' "list" of women he was allowed to sleep with; Joey later slept with a character played by Susan Sarandon. Ross referred to himself as "Cro-Magnum PI," Monica later slept with Magnum, PI. They try to get a table by giving the name "Winona Ryder," Rachel went to school with a character played by Winona Ryder. At one point they were trying to come up with the capital of Cambodia, and guessed, "Sean Penn," who they later met. Ross came up with the idea for "Jurassic Park," and Joey later met a character played by Jeff Goldblum. Most disturbing: Jessica Rabbit was on Chandler's list of celebrities he could sleep with, his FATHER was played by Kathleen Turner, who voiced Jessica Rabbit." And Elle McPhearson was mentioned in a list of women the guys thought about, seasons before she became Joey's roommate.
18. Why does Phoebe think Rachel would be too "vanilla" to kiss her college friend, when she's already seen her kiss Monica?
Which was how Monica and Rachel got their apartment back, something Phoebe was present for.