Throughout the series Chandler is paranoid about being Mistaken for Gay and generally more hostile about the topic than the rest of the gang. Of course, his earliest experience of someone being gay was his Dad, who announced he was gay on Thanksgiving, walked out on his family, started a very messy, painful divorce and repeatedly humiliated Chandler in high school. So his association with gay role models or the gay community, is filled with negative implications of abandonment and embarassment. No wonder he's so touchy about people thinking he's gay!
Chandler's pre-wedding freak out. Although it was triggered by the answering machine message, he then spends the whole night with his parents (who are seeing each other for the first time in years) and they do nothing but argue. It's Played For Laughs but imagine growing up in an environment with constant fighting. They probably brought back a lot of memories of his horrible childhood. Normally Chandler keeps his parents at a distance but he was seeing exactly what could happen to him. No wonder he got scared at that particular moment.
Why is Joey an actor? Because he grew up with 6 sisters, he probably had to do everything he could to stand out from the others and be recognised as an individual child instead of just another Tribbiani child. So his childhood was probably filled with him making jokes, singing songs, dancing around, trying to get attention by being as attention-grabbing as possible. So when he got older, OF COURSE he became an actor, because it's what he's been doing all his life.
Not only that, but why is Joey such a Ladies Man? Because he's an actor, he's spent his life having to live up to expectations, saying things that aren't true and pretending to be someone he isn't. So when he's in a bar talking to a cute girl, he can easily put on the charm, say all the right things and convince them to come home with him. Again, it's what he's been doing all his life.
Monica's obsession with marriage/weddings/babies seems excessive until you realize they are exactly the things her mother values and nags her about. It's also evidenced by Ross's obsession with getting remarried and staying so: marriage is very important in the Geller family. Monica wanted those things not just for herself but to finally gain Judy's approval. Turns into a CMOH/CMOA for Monica when you realize the concessions she makes (choosing a man her parents initially disapproved of, having a less fancy wedding, adopting rather than giving Judy biological grandchildren) were her breaking free of her mother's put downs and finding love and value in Chandler instead.
In TWW the embryos, before Phoebe takes a pregnancy test Alice asks "do you feel like taking a test? There's only one question!" And Frank laughs. This may just seem like a silly joke until you remember Alice is a teacher and Frank was her student.
Also in TOW the Embryos, there was one clear winner in the game of who knows whom the best: Ross. He wrote all of the questions/answers with the advantage of knowing Chandler since college (being 19 when he touched a woman's boob), growing up with Monica (her high school field hockey nickname), and having dated Rachel (not admitting that "Weekend at Bernie's" was her favorite movie).
When Ben is born, Phoebe tells Susan that he looks like her. While this is played off as Phoebe being a ditz, she's trying to make sure Susan feels included because Ben is her son, too. It's really sweet of her.
Chandler and Monica have amazing sex, which Monica outright describes as the the best she's ever had. The others, even Chandler himself are surprised by this as before he was implied to be pretty average in that department. Then you remember that Monica actually tutored Chandler in how to be better in bed so of course she'd think he's good because she taught him exactly what pleased her!
Brings a whole new meaning to "I'm the best because you made me the best."
In the pilot episode, Rachel resolves to change her shallow lifestyle funded by her father's money. The next time we see her, she's just gone on a huge shopping spree, laughing at the idea of getting a job, telling the others that she is qualified for nothing and how she was laughed out of several interviews and showing off her "I don't need a job, I have my new boots" boots. A casual viewing makes her just seem to be flighty and irreverent. Then you realize that she has an undertone of self-loathing, and she is actually trying to cope with the realization that she is entirely unequipped to live in the real world.
This is made even more amusing when later on in the series her sister does the exact same thing, only fails completely whereas Rachel grew more independent as time went on, indicating the significant shift in her personality over the seasons.
In the episode with Dakota Fanning Joey said that 'he's scared of little girl ghosts'. It's a nice call-back to Joey being freaked out by The Shining.
In one episode, Joey refers to something as "a moo point", explaining that said issue "is like a cow's opinion: it's meaningless... it's 'moo'." This may just seem like another moment of Joey's stupidity and him mis-hearing the word "moot" at some point in his past (and on the surface, it most likely is). However, in Zen Buddhism, mu is used to refer to meaninglessness. Which turns it from an Incredibly Lame Pun (also in character with Joey) to a Stealth Pun.
Ross is a mixture of Insufferable Genius and Honor Before Reason, but you wouldn't see why until you looked at him this way; Monica had to grow up always being The Unfavorite while Ross was the star child of the family and because of this, Ross was always praised for every single thing that he did while growing up and should Ross ever get into trouble, it would be safe to assume that his parents would do everything they could to quiet the mess so that Ross still comes out looking good. This leads to the present day Ross always trying to prove to his friends how he is right (whether it's on dinosaurs, who did wrong in a relationship, etc.) and how nothing is ever his fault. A good example of this is "The One With All the Secrets" where Monica told her parents Ross smoked pot in college (because Ross refused to admit it and had put the blame on Chandler back then).
On a similar note Ross and Rachel, who were both adored when they were growing up, failed to establish a steady romantic relationship but Monica and Chandler, who had a lot more emotional baggage, succeeded. Ross and Rachel were both extremely spoiled, Ross as the previously mentioned 'star child' and Rachel as her daddy's darling. Consequently they were both self-centered and egotistical which caused problems romantically. Monica and Chandler however grew up fighting for love: Monica suffering her mother's criticism's and Chandler being neglected during his parents divorce. So when they established a loving relationship it was extremely precious to them. They worked harder to hold onto it than Ross and Rachel who had always received support and attention.
At first Susan's dislike of Ross seems odd; as Carol realized she was a lesbian surely Ross poses absolutely no threat to Carol and Susan's relationship. However, as it becomes clear that Ross and Carol are Amicable Exes, it could be that Susan was worried Carol would realize she is bisexual and leave her for Ross, or at least that Susan was jealous of the attention (even non-romantic) that Carol gives Ross; Carol herself even admits that she does still love Ross and if it weren't for her being a lesbian they would still be together. Additionally, the timeline of Ben's conception and Ross's comment, "Carol and I had some great times before she became a lesbian...and once after" supports the idea that Ross and Carol conceived Ben after Carol left Ross. This explains both why Susan is hostile and why Ross seems to think he could have fixed the relationship with Carol despite her being gay.
In TOW Ross Can't Flirt, Chandler is initially concerned about Monica's self-confessed tendency to flirt with guys, but after hearing Ross's attempt he reflects "if all the Gellers flirt like this we don't have a problem." Chandler may be recalling his distant memory that Monica does in fact also flirt like that, as we discovered in an earlier flashback episode where she is trying to be flirty with kitchen items.
Joey's extreme reaction when people take food off his plate ("JOEY DOESN'T SHARE FOOD!!!") makes a lot more sense when you remember that he has seven sisters. Anyone who grew up in a big family can tell you that siblings frequently steal each other's food, sometimes even just to annoy each other, and protecting your plate is something you learn early on. It's especially telling that most of the people who try it in the episode are female - he has a learned fear of girls stealing his food!
In The Final One when Monica & Chandler bring the twins home, Rachel says "I'm sorry I wont be around to see you attempt to handle this", she's speaking for all of us in the audience.
It's reasonable to assume Joey picked up his knowledge of radiators from his father, who's a plumber.
In "The One Where Everyone Finds Out", note gang's reaction when they spot naked Ross in Ugly Naked Guy's apartment. Rachel reacts just a little earlier than everyone else, which makes sense—as his ex-girlfriend, she's seen him naked far more than any of the rest of them. Meanwhile, Monica freaks out and turns away to hide her face against Chandler's shoulder, which also makes sense—as his sister, she definitely wouldn't want to see him like that.
In "The One With Rachel's Assistant" Rachel hires a guy named Tag who is completely unqualified to be her assistant because he's attractive. However, Rachel initially got a job in fashion despite being unqualified and remembers what it is like to beg for a job to take a chance on her. While she says she hires him because he's handsome, she might also be thinking about paying it forward and giving someone else their start.
In an amazing example of Cross-over consistency, in The One Where Chandler Can't Cry Phoebe finds out that her twin sister Ursula has been masquerading as Phoebe to make many, many porno's. What makes this so brilliant? Ursula, who was Lisa Kudrow most prominent character long before Phoebe came around, was featured on fellow Must See TV sitcom Mad About You as the flighty waitress of Paul and Jamie's favorite restaurant. In that series finale, the show followed a now adult Mabel's, the lead characters daughter, documentary about her parents. During the credits of this episode, Mabel revealed the history of some of the characters between the then 1999 and her future era, including that Ursula, after having a successful career as a pornographic star, would eventually become the Governor of New York. This finale was aired before Friends season 6 began. The writers of Friends took a throwaway joke from one series, and made it an episode plotline in their own.
In 'The One Where Chandler Can't Cry', there's two possible reasons why Chandler is incapable of crying. The first is that he wasn't close to his parents, spent a lot of time in an all-boy boarding school, and was called names such as 'baby girl Chandler' by his gym coach. This could all add up to Chandler crying as a child, and being ridiculed and mocked for it so much that even into his adult life he isn't able to cry without fear of being mocked. Anyone who grew up around boys will tell you, they can be horrible and will look for any reason to call someone a 'girl' over something. But the second reason capitalizes on the first, it's possible that in his child mind, Chandler connected 'crying' with 'girly', and who did he know that was a man who acted 'girly'? His own father, who constantly humiliated him all throughout his childhood. It's entirely possible that the other reason Chandler never cries is because he thinks crying is 'girly', and that would make him more like his father, a person he dislikes so much he completely broke off contact with him for years on end
Chandler secretly being good at ping-pong makes perfect sense when you remember how long he lived with Joey and some of the rather extreme games they invented, as well as the foosball table that dominated their dining area.
Alternatively, Chandler would have had lots of opportunities to practice when he was at boarding school, which almost invariably contain a common room with a pool table, table tennis table etc (seriously - next time you speak to someone who went to boarding school, see how good they are at pool and/or ping pong).
In TOW Rachels New Dress Chandler decides he hates his name and declares he has no name so he temporarily assigns himself the name "Clint". One of Clint Eastwoods most famous roles was the Man with No Name from the Dollars Trilogy.
In the season 10 Thanksgiving special, Chandler and Monica have what amounts to a pretty terrible Thanksgiving, having worked hard to put together the meal that their friends were too busy to show up for, only for them all to arrive late, culminating in Joey crashing into the table of food and ruining everything. At first Chandler seems ready to unleash Monica on him for it, until Monica reveals the great news... they've been permitted to adopt a baby. But what makes this so brilliant is that every Thanksgiving episode in the show so far, this one included, has Chandler feeling unhappy with the holiday because of it being the day his parents announced their divorce when he was only 9. And yet, in the final series of the episode, Chandler gets a Thanksgiving where he's never been happier in his life
Why do Monica and Chandler have such a great sex life? Because Monica showed him how to sexually please a woman back when he was dating Kathy.
Arguably happens in-universe in "The One with the Breast Milk". When Ross refuses to taste Carol's breast milk, the others who have tasted it say it doesn't taste bad, and Susan says it tastes like cantaloupe juice. Ross is bewildered by this. Considering there'd only be a few reasons why Susan would have tasted it... and of course, it wouldn't be out of character for Ross to jump to the conclusion that doesn't involve Susan just tasting it the way everyone else did.
Judy Geller repeatedly nags Monica about having children in early seasons: She's drives Monica to tears, says Ross is the only way she'll have grandchildren and freezes Monica out when she discovers she's not pregnant in Season 8. Wonder what her reaction was when she discovered Monica and Chandler were infertile? Luckily Monica herself had apparently gotten over pleasing Judy by that point in her life, as her relationship with Chandler and successful career became forefront to her mind.
A minor one from "TOW The Dirty Girl". Cheryl lets her hamster, Mitzi, roam around free in her biohazard of an apartment, and comments that "I hope she's okay, I haven't seen her in a while". Later, when something starts rustling in the garbage, Ross clobbers the hell out of it. To Cheryl's relief, it turns out to be just a rat, not her missing hamster. However, rats are notorious for hunting and killing smaller rodents, and they rarely travel alone. Mitzi's chances aren't good.
More like fridge sadness — Phoebe comments on her mother's attempts to "save" her from the endings of sad movies as being incongruous with the fact that she committed suicide, but if her mother was suicidally depressed or the partner of a depressed person and living in miserable circumstances, it makes sense that she'd want to shelter her kids from even fictional downer endings, the only kind of sadness she might have felt she had control over.
Furthermore, Phoebe recounts how she cried for days after seeing Bambi, which she saw mere days before her mother's suicide, indicating her mother was probably past caring what kind of movies her kids watched (or alternately, thought it would be an appropriate prelude to what was about to happen,) and a distinct possibility that some well-meaning friend or neighbor overlooked all of this when offering to take Phoebe and Ursula to a nice Disney movie.
At the end of "The One With Russ", Julie and Russ hook up. Terrific, she's a sweet and lovely girl who deserves a nice guy. . .except that she's probably making the exact same mistake Rachel was making throughout the entire episode. And doesn't Russ deserve better than being used as a Replacement Goldfish—TWICE?
Remember that crazy girl who was in love with Dr. Drake(the character, not Joey)? Imagine how she felt when Drake died in the show.
In 'The One With the Prom Video', Monica watches the rest of the prom video while the credits are rolling, only for the video to change to a homemade sex tape of her parents. However, what makes this worse is that we see the camera is actually zooming in, meaning that someone had to be controlling the camera ...
The "Where Are They Now?" Epilogue in Mad About You reveals that Ursula Buffay eventually becomes governor of New York, while this series gives extensive reasoning to believe that Ursula should be clinically diagnosed as a sociopath. Having someone like that as governor of a state is very worrying.
The first time Ross and Rachel meet on the show, an umbrella accidentally opens inside as Rachel and Ross move to shake hands. The umbrella opens up between the two, which is possibly foreshadowing the bad luck their relationship would have.
At the end of "The One Where No One's Ready", Rachel comes out in a lovely pale green dress perfect for the occasion. This took her a very short time to pick out, despite the fact that she spent so long beforehand trying to decide between different dresses and outfits and aggravating Ross, and had dressed down before getting to the green dress.
In the last episode, Monica and Chandler are moving to the suburbs to raise their kids, and Ross and Rachel are getting back together and raising Emma (and any more that come along) in the city. Why didn't they just move into the apartment so that Ross could stop sub-letting Ugly Fat Guy's apartment? The place was rent-controlled, probably not like UFG's sub-let, and all of them stayed there at one point of their lives (Ross was in the spare bedroom during one summer from college.)
Sure, it made a good ending picture, moving from the keys on the counter to the frame on the door, but c'mon, a rent-controlled apartment in NYC? Even if Ross and Rachel had some money, which they should have by the end of the series since they had good jobs, it would still be a lesser cost.