Subverted in an episode where the lie works perfectly, but Sheldon overcomplicates it when he notices minute flaws in it. The lie never actually falls apart.
Subverted in "The Recombination Hypothesis" Leonard ended up having to explain to Sheldon why he was returning to the apartment at 3 in the morning, when Sheldon was getting out of the bathroom. The real reason was Penny dragged Leonard over to her apartment to have sex and start seeing each other again but Leonard didn't want to tell Sheldon about it. So it slowly got more and more implausible as Sheldon poked holes into the explanation, until Leonard actually had some evidence to back up his claim (an asthma inhaler brought up in the previous scene).
Felony Misdemeanor: In-universe and Played for Laughs. When Leonard is invited to see the Large Hadron Collider in Switzerland on Valentine's Day and insists on making it a romantic holiday with Penny, instead of taking Sheldon as was agreed to in the Roommate Agreement, Sheldon is very angry and plays a driving game with him called "Traitors" where he names three historical traitors and Leonard is to put them in the order of the magnitude of their treachery. First round: Benedict Arnold, Judas, and Dr. Leonard Hofstadter. When Leonard protests against being included in the same category as these men, Sheldon even hints that Judas ranks somewhere below Leonard.
When talking about the horrible things that would happen at his birthday parties, Sheldon confessed to Penny with great anguish that he got a motorized dirtbike instead of a titanium centrifuge. Sheldon simply could not understand what child would like such a gift, and was genuinely perplexed when Penny said that most kids would love it.
Sheldon: If you fail at this relationship, and history suggests you will, then we risk losing the medical officer our landing party has always needed. Leonard: What landing party? Sheldon: You're Kirk, I'm Spock, Wolowitz is Scotty, Koothrappali is the guy who always gets killed [looking at Leonard's doctor girlfriend at the time] and now we've got McCoy.
Although the trope itself is generally averted (see Four-Man Band).
Sheldon started off as slightly more neurotic and less interested in socializing than Leonard, but quickly grew to where his Neat Freak and Schedule Fanatic traits were more dominant. In addition his disinterest in socializing was eventually explained, in part, by his Asexuality.
An inversion of this trope is done in the Whole Episode Flashback to when Leonard and Sheldon first met. The Sheldon of the series has all sorts of quirks but still makes awkward attempts at social interaction and understanding how normal people think, the Sheldon of the flashback was basically a flanderization of his current personality where his Control Freak and Insufferable Genius mannerisms were about all he was. While not really elaborated upon, it's suggested that being friends with Leonard is the reason Sheldon of today is even remotely workable.
Raj started off just as nerdy as the rest, his primary quirk being so shy he couldn't speak in front of women and a few jokes around him being a Funny Foreigner. His shyness and the Homoerotic Subtext in his relationships with the guys (since he rarely talks to women) eventually grew into him being Ambiguously Gay with a lot of Innocent Innuendo and very rarely is there not a joke about him being the Token Minority.
In addition, despite being unable to speak to women except when drunk, Raj is initially portrayed as the most likely of the guys to get girls — for example, Raj is the only one of Sheldon's friends that Missy is actually attracted to — but this is gradually phased out, so that by Season 6 he's terrible with women even when he can speak to them; even when he started dating a woman more socially awkward than him, he scared her away, and when they ended the season by showing him able to talk to women while sober, up.
Subverted with Amy. Initially she's just as socially awkward, robotic and autistic as Sheldon, if not even more so, but by the time she becomes Sheldon's girlfriend in the middle of Season 5 a large part of that has been dropped and she's become much more normal.
If anything, they highlight her less obvious traits. At first, she's pretty much distaff-Sheldon. As the series continues, Amy's defining trait becomes that unlike Sheldon, she craves the approval of others, enjoys interactions with the group, and longs for sexual contact — similar process, but she contrasts, rather than exaggerates. Reversed polarity Flanderization
Bernadette, when she was first introduced, was very nice and polite, though rather ditzy. Occasionally the writers would have her say something uncharacteristically mean or violent, the joke being that because she was normally so sweet, seeing her act that way was funny. As the show went on though, these outbursts became more and more common, and the Bernadette of later seasons is a very short-tempered and competitive person. The ditzy aspect of her personality was dropped, probably to differentiate her more from Penny, and she eventually Hand Waved it by saying she initially acted dumb to make her boyfriend Howard feel smart.
The local Comic Book Store owner, Stuart, was originally just a very normal guy who successfully asked Penny out. It was a key plot point that in terms of being a decent, normal guy he was virtually identical to Leonard. While he remained a friendly guy he later gained some neurotic ticks, low self-esteem and has a lot more trouble talking to women than before. The change can probably be explained that "nice, normal guy" doesn't leave things too open for comedy and they wanted him to stand apart from Leonard.
In the case of Stuart, it's implied in the show that he hit a string of bad relationships in addition to financial problems and health issues. Getting crushed by Penny (who said Leonard's name while they were making out) in addition to living in the comic book store probably destroyed his self-esteem.
Raj: "I still wear mine when there's a nip in the air."
Flipping the Bird: Played with. After Sheldon made an insult about Wolowitz's robotic arm, he gave it a command and it held up the peace sign, which confused Sheldon and Howard tries fixing the code.
Sheldon once quoted the Rubiyat to Penny after she made him miss an autograph signing with Creator, explaining that it was too late to make reparations. Penny, confused, thought he was giving her the finger
Sheldon: "The moving finger writes, and having writ, moves on."
Penny: Did he just somehow give me the finger?
In one episode, on a road trip, Sheldon irritates Howard over a walkie talkie to the point that Howard flips him off off-camera in the car ahead
Sheldon: Radio contact is sufficient, no need to extend your middle finger
Food and Animal Attraction: In one episode, Sheldon is chased by a vicious dog because it can smell the hot dogs Sheldon was hiding in his pants.
Forgot to Pay the Bill: Penny asks if she can watch TV in Sheldon and Leonard's apartment because there's nothing but static on her TV. Howard asks if she paid her cable bill and Penny says, "Ugh, you sound just like the cable company."
Four-Man Band: Even lampshaded when Sheldon determined the roles of this trope.
Leonard: You put ground-up moth in my food?! Sheldon: For Science!!
Freaky Fashion, Mild Mind: Alice from "The Good Guy Fluxuation" was a female geek (very rare on the show) and dressed in a combination of punk rocker and goth, along with a noticeable tattoo on her chest and a wide assortment of piercings. She turned out to be really friendly and well-mannered in addition to her geeky passions.
Freeze-Frame Bonus: Howard's mother, never actually seen before on the show, can be seen from above in the zoom out from Howard's wedding in the Season 5 Finale.
Freudian Excuse: Averted by Raj, when he decides to be a douche for no apparent reason on the penultimate episode of season 4.
Raj (amused): Youíd think itís because my parents didnít love me, but actually they loved me a great deal.
The reason why Leonard is so needy in relationships, likely comes from the fact that his mother maintains a cold detachment from him and treats him as more like a test-subject. His need for intimacy resulted in him building a hugging machine as a child.
The worst part is, his father used to borrow it.
Freudian Trio: Confirmed by Word of God, the Penny/Leonard/Sheldon relationship was designed to be like this. Sheldon is The Spock, who represents "logic" and the aspirations of science over all else. Penny is The McCoy, who represents "emotion" and the promise of a full life to experience. Leonard is The Kirk, who is torn between those two worlds.
Amy incidentally describes the trope when depressed and analyzing her relationship with Bernadette and Penny, but done in her own neurobiology terms. Penny is the creative and spontaneous right half of the brain while Bernadette is the scientific and analytical other half. Amy is the one of the group caught between the two halves, but her comparison comes out to her being a tumor.
FridgeLogic/FridgeHorror: In-universe, Raj's specialty is pointing this out, such as remarking that, since zombies only eat living brains, they would ultimately run out of food, but, being undead, cannot starve to death, leading one to wonder why they need brains in the first place. Or that, on Pandora, their ponytail is "like their junk, right?" and so, if one is a pterodactyl or a horse, one ought to be very nervous aroundJames Cameron. For meta/fan examples, see this page
Friendship Moment: With regularity. They like to prank each other and often don't get along, but all the guys came from the geek end of the social pool and so they've banded together really tight. Sheldon, in particular, did not have many friends growing up and when the moment comes he is very grateful for the friends he has. This happened as early as the second episode, where Penny freaked out over a violation of privacy (Sheldon cleaned her apartment while she was sleeping). After thinking it over she forgave them, and even told Leonard everything was okay when he came over to apologize.
Friends Rent Control: It's not as bad as it could be, since they aren't living in a luxury New York suite, but a smaller building with a broken elevator in Pasadena. Sheldon mentions that if he could afford it he wouldn't have Leonard as a roommate. Penny seems to mostly afford her apartment on a waitress paycheck (and tips) with little trouble, at least until it's plot relevant. Unlike other examples of this trope, rent issues are relatively common. Penny has had to leave work from time to time because of the guys, and she always points out that losing a day's pay is not helpful.
It might have more to do with the fact he needs Leonard to drive him to work than to pay for the apartment. He seems to have more than enough money as he doesn't cash his paychecks. Leonard and Sheldon are both single, degreed professionals who should logically be able to afford their apartment with little difficulty.
A quick Google search shows that one bedroom apartments in buildings the seem classy enough to repair an elevator within a decade of its breaking/exploding would run $12,000 to $18,000 a year, two bedrooms about $18,000 to $24,000. We can probably assume that the gang lives at the lower end of the scale. More web research shows a waitress could make $24,000 and up, which would fit with her struggling to get by. On the other hand, at Caltech, even instructors (below professors) make about $45,000, Assistant Professors and above around a hundred grand and up. Overall, I'd say that more than "not as bad as it could be", this trope is completely averted.
Moreover, Sheldon has both been at CalTech longer and is higher on the career ladder than Leonard.
All of them (minus Penny) also seem to have ample money to burn on collectibles, trips, costumes, and whatever else catches their eyes at the time. Leonard and Sheldon might just want to pay as little as possible in rent to free up their income for other things.
When Sheldon lends Penny the money she needs to pay her bills he tells her that he's not worried about when she'll pay him back because he has more than enough money to pay his bills and any new gadgets he buys and still have some left over, claiming that he only needs 47% of his income. Sheldon could easily afford to rent the apartment on his own but chooses not to for various reasons
Friends with Benefits: Discussed, with Sheldon not really understanding the concept. "What exactly does that expression mean, 'Friends with Benefits?' Does he provide her with health insurance?"
Sheldon: Are you and Leonard "Friends With Benefits?" Penny: No! Did he say we were? Sheldon: Leonard said nothing, but who knows what goes on over here when he pretends your mail was misdelivered. Penny: What? Just mail, no benefits.note In a Hilarious Outtakes moment, Kaley Cuoco accidentally switched the phrase, saying "Just benefits, no mail... wait?
Full-Name Basis: Amy is often referred to by her full name, Amy Farrah Fowler.
Fun T-Shirt: There's even a website that keeps track of the characters' shirts and where you can buy them. In one episode, a gag was about Raj having a shirt with a speaker built into it. It could play everything from the Imperial March to the Final Jeopardy theme. You can get it here.
Fun with Acronyms: In "The Bat Jar Conjecture" the guys decide to enter the university's Physics Bowl and have a debate on what to name their team. Sheldon prefers the Army Ants while Howard suggests Perpetual Motion Squad. Later, Sheldon has a fallout with the others and actually enters the Physics Bowl against them... so it's AA vs. PMS.
Sheldon's suggestion for the name of Leonard's iPhone app.
"Suprisingly Helpful Equation Link Differential Optimise Numerator"
Funny Background Event: In "The Financial Permeability," Raj runs to the bathroom after Penny yells at him, with Howard explaining that stress gives him a nervous bladder. He later comes back just as Penny starts yelling at Sheldon — then turns tail and runs back.
Gallows Humor: In "The Cooper Extraction" Howard is helping decorate a Christmas tree. It is mentioned his mother would likely die at the sight of it. Bernadette agrees and they take photos of Howard.
Gamer Chick: Penny isn't a gamer, but in S1 Ep07, "The Dumpling Paradox", she fills in for Howard for the guys' Halo night, and the first time she picks up an Xbox controller, she manages to outclass all of them on her first try. And yes, the guys are 30-year-old geeks who play Halo religiously. However, considering Penny's more rounded characterization, this is surely less Positive Discrimination and more Rule of Funny.
Penny: (As Sheldon tries to leave for his bedroom) Wait, wait! Sheldon, come back! You forgot something! Sheldon: What? Penny: This plasma grenade! (Sound of large explosion) Ha! Look! It's raining YOU!
Sheldon clearly doesn't believe in this trope.
Sheldon: I don't know how, but she is cheating. Nobody can be that attractive and this skilled at a video game.
S2 Ep03, "The Barbarian Sublimation," also has Penny getting addicted to Age of Conan.
Geek Physique: Both Sheldon and Howard are very skinny, and once Howard boasted of having 3% body fat (described by Raj as a "Human Chicken Wing"). Raj and Leonard are of average size (though there is a reason we rarely see Leonard barechested or in simple T-shirts, as Johnny Galecki is in pretty good shape). The only "geek" on the show who is overweight is the minor background character "Captain Sweatpants."
Geeky Turn-On: To be expected given the premise of the show. One episode had Raj and Sheldon together with Sheldon holding a Green Lantern Power Battery and it actually attracted the attention of a couple of girls, thinking it was cool. An unfortunate side-effect of this trope shows up when Leonard and Penny are together in bed and Penny references a line from Star Wars and even knew the exact movie. Leonard was so excited being with her in that moment he said a premature "I Love You" and it caused a storm of awkwardness that lead to them breaking up.
When dating, Penny suggested that she and Leonard make out on Sheldon's spot on the couch. This was seen as quite a taboo thing to do.
Amy figured that she could best assimilate herself as a romantic interest to Sheldon by influencing him with all the things that he loves. Thus they have a romantic evening with music from Super Mario Bros., Strawberry Nesquik and spaghetti with hot dogs cut up in it. Sheldon surprised himself with how well it was working, and the subplot ended with Amy dressed up as Nurse Chapel and "playing doctor" with Sheldon Star Trek-style.
"The Holographic Excitation" had Penny admit to Bernadette and Amy that she really did not understand what Leonard does as an experimental physicist. After some prodding she surprised him at work and asked to see some of his experiments. When he gave her a short presentation musing on a theory of the universe she was awestruck and said "Sometimes I forget how smart you are." They ended up fooling around in his lab and apparently repeated the pattern of science project/sex over the next few days.
"The Egg Salad Equivalency" ends with Penny revealing she bought a pair of nerd glasses in order to invoke this. Leonard's skeptical at first... and then she puts them on.
Penny: Molecules. Leonard: Oh my god you look so smart and hot!
Genre Savvy: Penny manipulates Sheldon into re-rolling dice by pointing out "Doubles. Roll again."
Getting Crap Past the Radar: The show actually gets away with a lot of surprising jokes. One memorable joke comes from "The Pants Alternative".
Penny: So, Sheldon, will you let us be your X-Men? Sheldon: No, the X-Men were named because of the beginning letter of the last name of Charles Xavier. Since my last name is Cooper, you will be my C-Men. (the other characters get very quiet) Raj: (later in the episode) How can Sheldon be nervous? He's surrounded by his C-Men!
What about from "The Plimpton Stimulation"? A couple of jokes from that episode...
Sheldon: What am I supposed to believe? That you somehow tripped and fell into her lady parts? (later) Penny: No, no, you don't have to drive me to work. It's OK! It's not like I'm afraid you're going to trip over and get me pregnant.
Oh, and the end where Dr. Plimpton tried to get the boys into a foursome.
Don't forget "The Bat Jar Conjecture". The team was called PMS. What made this hilarious was what the back of the shirt said. We can go all night. Howard proudly shows off his shirt.
In the fifth season finale the group learns that Leonard stupidly proposed to Penny in the middle of sex. Howard's response was "Did you get on one knee or were you already there?"
From the same episode:
Howard: Close your eyes and hold out your hands. Bernedette: Come on, Howard, I'm not falling for that again.
In "The 43 Peculiarity" Leonard was worried over Penny spending time with a male classmate and Sheldon suggested that if the guy was a skilled hypnotist Penny may be performing sexual acts on him with her thinking she is just "a chicken pecking for corn." Upon getting a very disturbed look from Leonard, Sheldon "helpfully" pantomimes the action.
In "The Good Guy Fluctuation" Leonard gets hit on by a cute girl in the comic book store who writes her name and number on his hand, leading to this:
Leonard: Sorry, my palm's a little sweaty, what's that word? Alice: Alice. Leonard: Oh right, your name. That makes so much more sense than penis.
In "The Closet Configuration" Sheldon is straightening out Penny's closet and asks if she has a dog, because he found what appeared to be a "battery operated chew toy" in there.
Sheldon: "I still don't understand why no one else bid on the (what he thinks is a miniature) time machine". (Switch to the foursome standing around the recently delivered full-size time machine) "I understand why no one else bid on the time machine."
"Fish Guts Displacement" has Howard asking Leonard and Raj if they knew how to fish, which they laughed over. Howard then asked "Who are we going to find that knows how to do this kind of manly stuff?" Cut to the guys at Penny's door, who opens wearing an oversized T-shirt and eating a slice of cold pizza. "What?"
Girlfriend in Canada: Amy Farrah Fowler admits she once told her family she had a boyfriend who was a miniature horse breeder. The lie unraveled when she was asked where they met. She panicked and said "Woodstock".
Averted, when a very tipsy Amy gave Penny a mouth kiss ("Come here, Bestie, give me some sugar") it was not only very underplayed but Penny even gave an embarrassed laugh after it happened. In addition, there wasn't any rising laughter by the Laugh Track.
A similarly understated moment happens when Penny and Bernadette discuss the awkward things Amy likes to talk about with them such as painting fertility symbols on Bernadette's naked body as being a wedding ritual. The guys noticeably quiet down after they say that, with Raj in particular (being silent anyway) subtly staring off into space.
Give Geeks a Chance: As the show has continued it has actually started poking holes into this trope with the relationship between Leonard and Penny. Both are worried that the other will grow tired of the other, Leonard for the fact Penny is so much more attractive than him and Penny for the massive intellectual gap between them. Then the show tries putting it back together showing both Penny trying to understand his work and Leonard dealing with his insecurities.
Godzilla Threshold: In one episode involving a war between Sheldon and Penny, Leonard gives Penny what is more or less (as he described it) Sheldon's kryptonite. His justification for doing so is that it would "cut five years off the war and save millions of lives". Said kryptonite being the phone number of Sheldon's mother.
"Good Luck" Gesture: In "The Holographic Excitation", Stuart says to Raj that he tries to use Halloween parties as means of meeting women. He crosses fingers and says: "The ninth is the charm." Hang in there, buddy!
Goofy Print Underwear: On one episode Howard talks Leonard and Raj into being his wingman at a bar. They all change out of their standard Superhero symbol boxer shorts .... just in case.
Gray and Grey Morality: In "The Speckerman Recurrence," Penny, Bernadette and Amy have a change of heart after nearly taking clothes from a donation bin. Bernadette goes back for suede boots, screaming her justification, "It's OK, I serve soup to poor people!"
Groin Attack: Sheldon's sister's method of keeping Sheldon in line.
Penny administers one to the guy who hacked Sheldon's World of Warcraft account in "The Zarnecki Incursion".
Howard sets Leonard up with a date that knows 100 ways to rip a guy's nuts off. She's not shy about demonstrating them in a restaurant.
Penny threatens Amy with this in one episode after the latter accidentally hits her in the nose. This is after Amy had gotten a bikini wax for the first time.
Hair Today Gone Tomorrow: In the flashback episode late in season three, Leonard had long, wavy locks, Howard had a Jewish Afro and Raj had something of a mullet. Sheldon was the only one with the same hair-style, and with the exception of Howard their current looks are big improvements.
Halloween Cosplay: The group, plus Penny's then-current boyfriend Zach dress up as the Justice League of America for a costume contest
Amy: If your friends are unconvincing, this yearís donations might go... say, the geology department. Sheldon: Oh dear, not the dirt people! Amy: Or worse, it could go to... the liberal arts. Sheldon: No. Amy: Millions of dollars being showered on poets, literary theorists and students of gender studies. Sheldon: Oh, the Humanities!
In one early episode Penny is seen eating an entire tub of ice cream while crying her eyes out due to a breakup.
Heel-Face Turn: In "The Russian Rocket Reaction," one of Sheldon's mortal enemies crosses himself off of Sheldon's list.
Height Angst: Leonard is always complaining about how short he is, and is often mocked for it. Howard is also shorter than average and is made fun of for that, but Leonard is the only one who openly angsts about it.
Helium Speech: Kripke fills Sheldon's office with helium while the latter is on call for an NPR interview. The pitch of his voice increases throughout the entire interview.
Her Code Name Was Mary Sue: The episode where Penny becomes addicted to Age of Conan everyone's characters were clearly named after them: Sheldon was Sheldor (The Conqueror), Penny was (Queen) Penelope and Howard was... Sir Howard of Wolowitz.
Heroic BSOD: Sheldon when he discovers that Leonard, Howard and Raj lied to him about the results of his experiments at the North Pole after he has already boasted about changing the face of physics to everyone, earning him a ton of ridicule when he has to print a retraction.
Then Penny's attempt to cheer him up, by comparing his situation to when Young Spock was teased for being half-Vulcan, leave him in further despair when he discovers even she has seen Star Trek before him.
A great example was the episode in which Sheldon gives his reasoning for hating gift-giving, in that he hates it because he always assigns a dollar value to any gift and does not want to feel like he is in someone's debt because they bought him a more expensive gift than he bought for the person. So, his solution for Penny is to go to a gift-basket store and buy a variety of baskets in various price ranges so he can reciprocate properly. Penny's gift to Sheldon? A signed, used napkin from Leonard Nimoy. When Sheldon realizes what she has given him, he goes to his bedroom and returns with all of the baskets. He has his BSOD moment when he thinks in his mind that what he has given to Penny does not even come close to her gift value-wise. He then gives Penny a hug!
"Geology is not a real science!", with Platoon style "death"
Heterosexual Life-Partners: Howard and Raj argue like a married couple, and are generally paired together in team activities and usually serve as each others "wingman." Leonard and Sheldon are a more mild version, as Leonard can only stand Sheldon for limited periods of time.
Hilariously Abusive Childhood: Leonard, to the point where the government would have taken him away from his mother they known about the psychological torments she put him through. Sheldon to a lesser extent, being more of a case of a loving family to which he was well out of step (as evidenced by his complaints about not receiving a titanium centrifuge as a child, as no child would wants a dirt bike). Though all the male characters appear to have been regularly bullied in school.
Hilarious Outtakes: You can only imagine the slip-ups that occur due to all of the terminology the characters throw around. Jim Parsons in particular had no end of trouble with the "Rock, Paper, Scissors, Lizard, Spock" explanation, just by the sheer length, the hand motions, timing and not letting the audience laughter throw him off.
For a treat to their studio audience they organized a Flash Mob, dancing to "Call Me Maybe" and other songs.
In preparing for another take the director went up to guest star Bob Newhart and gave him a laundry list of things he needed to reset and do. While he walked off set Newhart joking exclaimed "I'm 83! What the hell do you want from me!" which got an ovation from the cast and audience.
Hollywood Dateless: We are supposed to believe Leonard is awkward with women, and in a way, he is. However, his dating history includes many hot women — Penny, Dr. Stephanie, Joyce Kim, Leslie, and now Priya — so one has to wonder why would he think he is unlucky with women.
Also part of his rather obvious Character Development during the show is that he gets better around women thanks to spending time with Penny. Same with Howard. Averted with Raj, who still can't speak to women who aren't relatives without drugs.
Until Season 6, when he finally gets over his selective mutism after being dumped.
Hollywood Nerd: Type 1 is first played straight in the pilot where Leonard pines after Penny, and he and Sheldon get bullied and humiliated via Comedic Underwear Exposure trying to get her TV back from her stereotypically Jerk Jock ex-boyfriend. Later, we learn that scientists, academics, comic book geeks, and Wil Wheaton are perfectly capable of picking on each other without outside help.
Hollywood Pudgy: Poked at when the guys managed to convince Penny and her date Zach to join them at a costume party as the Justice League of America. Penny got upset over things both overt and subtle and refused to go, and Sheldon tried to convince her to come by claiming to know why she was upset... that she thought she looked fat in the Wonder Woman costume. That was obviously not the reason she was upset (and clearly not the case in the show) but Penny then started to worry that maybe she did look fat... and Sheldon tried to "comfort" her saying it doesn't matter since Amazons were supposed to be "beefy gals."
Invoked again by Sheldon when, after Penny takes the last dumpling, supposedly one reserved for a guest of honor, he curtly tells her, "I've seen your mother. Keep eating." The downcast look on Penny's face says she really took that one to heart.
Averted as practically the poster child for the trope, Sara Rue, guest starred in a short story arc in season two as a Love Interest for Leonard (and briefly Howard). She is depicted as being exceptionally attractive and that Leonard was lucky to have her.
Leonard's mother has never been wrong about anything in her psychiatric evaluations of the cast, therefore her ideas about Howard and Raj must be correct as well.
There's also some between Amy Farrah Fowler and Penny. For example, in "The 21-Second Excitation", Amy thinks that at slumber parties, girls often experiment with lesbianism, and tries it on Penny. It is increasingly overt as she makes references to Penny's bosom defying the laws of physics and brings up "bridesmaid traditions" that involve stripping down and washing each other.
This goes all the way into the DVD Special Features. In "Set Tour with Simon and Kunal" they talk about how the stairway set doesn't have much space down below, forcing them to cuddle close to not appear on camera (complete with demonstration). And when the two find Johnny Galecki in the main apartment set, they end up snuggling together while asleep.
Taken to ridiculous lengths in the second episode of season 5 when Raj and Howard use a simulator to make out with each other.
Later in season 5, Howard mentions that he can't imagine receiving a massage from another man.
Raj: Really? What was I doing to your neck last night while playing Xbox?
Leonard ends up taking Raj to Switzerland on Valentine's day, who squees at discovering the champagne and chocolates meant for Penny.
Leonard: Yeah, sorry. I forgot about all of that. Raj: But I never will.
Katee Sackhoff: Howard, do you have latent homosexual tendencies? Howard: Of course not! George Takei: So you say... yet here I am!
Pretty much every scene Raj and Stewart have together in season six....
Honesty Is the Best Policy: In "The Indecision Amalgamation" Raj ends up getting two dates, one from the redhead Emily and the other from his ex-girlfriend Lucy within a week of the other.Unable to cope with what he considers wrong, he tells Emily the truth and about how his relationship with Lucy never reached consummating it with sex. Noting she did know things could get weird on the date, she is smitten by his need for such a level of honesty, she continues the date with him and would have a few more. Averted with Lucy who didn't take the news well, but that wasn't seen.
Honey Trap: As found out through flashbacks, Joyce Kim.
Humiliating Wager: The guys lose a bowling match and therefore have to show up at the comic book shop dressed as superheroines.
Humorless Aliens: Frequently referenced when people call Sheldon an alien, ask what planet he's from, etc.
Hybrid Monster: Sheldon mentions a desire to create a Griffin and a "Dog-topus". Mankind is thankful he hasn't... yet.
Hypocrite: Lampshaded. Leonard complains about a co-worker and stating how his achievements aren't so impressive. Said co-worker then comes over and asks if Leonard wants to help him with a project that Leonard is completely excited over. After the co-worker walks away his friends look at him.
Leonard: What? Haven't you ever seen a hypocrite before?
Sheldon once claimed that Barry Kripke "lacks the basic social skills that we take for granted", accused Leonard of having Narcissistic Personality Disorder and when Howard refused to drive him home because he didn't want to use a hospital bathroom, Sheldon complained that friendship is not supposed to be "all give and no take".
Sheldon calls Kripke childish for having called dibs on Professor Rothman's now-vacant office... roughly thirty seconds after having done so himself. When Leonard points this out, Sheldon irritatedly tells him to "Shut it!"
When on a "non-date" as friends hanging out, Leonard and Penny argued over the things they hated doing together (Leonard doing karaoke at 2AM and Penny watching a documentary). But when trying to strike up a conversation with other people, they used those same things to make themselves seem more interesting.
When Sheldon points out that Hindu customs mean that Raj does get to say who Priya dates. Also that by disobeying it, she'd be "reborn as a jackal with many diseases". She counters that by eating beef, Raj would have to "live with a cow for several months and drink their urine".
Raj: Some of it makes sense and some of it is crazy, the point is I forbid you to date Leonard!
Amy once said that Penny and Leonard are the strangest couple ever. While they have have some unusual quirks because of the massive educational gap between them, Amy and Sheldon's relationship is bound by a written contract.
One episode had the characters reworking the battle of Gettysburg with additional units ranging from real-world military units to Hindu gods. The humor value of the discussion was ruined somewhat by a lack of research that had Sheldon accepting Leonard's spurious argument that Middle-Earth's Orcs "are magic" and so would defeat Superman, who is vulnerable to magic.
Also in The Big Bang Theory, the guys start to debate whether the White Witch or Billy the Kid would win a fight in a card game, and are persuaded to buy the cards to find out, telling themselves off for doing so.
Iconic Sequel Character: Amy and Bernadette were introduced only in Season 4, and have since become part of the core cast.
I Have This Friend: While Penny admits it's her own story, she tells Sheldon in "The Flaming Spittoon Acquisition" about how she never took the chance to tell a guy about her feelings for him until it was too late. It's fairly obvious to the audience she was talking about Leonard (the episode even shows her with signs of depression by drinking excessively) but Sheldon mistakes "the guy" she liked as being him, which she corrects him for.
Penny shared another story with Sheldon that was expressly not her, but a co-worker who was also an actress and got a toothpaste commercial she also auditioned for. With the details of "work at the cheesecake factory" and "fake blonde hair", Sheldon continually assumed it was really her, although the point of the story (being happy for a friend despite being jealous) would have been lost if it was.
I Know Mortal Kombat: Scattered around various episodes are claims of knowing how to perform a certain sport by practicing with video games. Sometimes not even that, Sheldon claims to know how to swim by practicing in the living room.
Inverted in that Sheldon claims to be good at archery on the Wii because his father taught him actual archery.
This comes up a second time in the sixth season when they start dating again and Raj finds out she's never said it to Leonard. When she was in an exasperated mood in "The 43 Peculiarity" she said "You know I love you, so could you please relax because you are driving me crazy!" and they both freeze as they realize what she said. When Leonard leaves for the summer at the end of the season, she instigates the "I love you" and he responds in kind.
An interesting contrast is shown during the time they were broken up, when Penny recruited Leonard to have gotten back together as a ploy against her dad. Leonard had a blast with the play acting and generally made Penny suffer for the idea, including a sugary "I love you" that forced Penny to say "I love you too" in order to keep up the deception. Because it was a sham there wasn't any repercussions for the phrase.
Important Haircut : Penny sports new short hair in Season 8, the beginning her "more serious" character development, including getting a better paying job.
Insomnia Episode: In one episode Sheldon is unable to sleep as long as he's left a specific science problem, one he's having a lot of trouble with, unsolved. Over the course of the episode he steals peas, then makes diagrams with marbles, and when those are not big enough he breaks into a generic Chuck E Cheese type place to use the balls from the ball pit.
I Owe You My Life: When Sheldon saved Leonard from the rocket fuel explosion that destroyed the elevator, the main reason Leonard lets Sheldon get away with as many demands as he does.
Howard: "DO YOU REALLY THINK YOUR LIPS IN MY EAR IS HELPING???"
When Penny and Leonard had a fight, Sheldon goes to Penny to try and rectify the situation, only to end up confessing to her that Leonard is highly annoyed by some of her habits but has never told her because, according to Leonard, Penny "is overly sensitive and has a temper". Penny's response is to tell Sheldon to tell Leonard to drop dead.
Howard often responds to his mother's treating him like a child by reminding her that he is 26 years old. Followed by agreeing for her to bring him a Popsicle.
Leonard: You're a big boy, you'll figure it out.
Sheldon: Don't talk to me like I'm a child. Now take me to return my Star Wars sheets!
Subverted, when playing a 20 Questions game Raj managed to guess Leonard's item of C-3PO by saying "Does he look like a shiny Sheldon?" Sheldon perks up as Raj guesses correctly and appears at first miffed, only to say that he is flattered but doesn't see the resemblance.
In defense of having Amy around, Sheldon once listed off all the things he had to silently put up with having Penny around. Leonard didn't argue any of the things listed, but got rather upset with the "silently" part.
I Think You Broke Him: In one episode, Penny is giving Sheldon acting lessons, and they are acting out a Star Trek fanfic Sheldon wrote when he was 10. He is acting as his mother, and begins to improvise, relating it to his real life. When he breaks down and starts crying, Penny calls up his mother and says, "Mrs. Cooper? Hey, it's Penny. Yeah, I think I broke your son," and hands the phone to Sheldon. "Mommy, I love you!" *sobs* "Don't let Spock take me to the future!"
Somewhere between this and Can't Spit It Out, Penny doesn't want Leonard to leave to go to the North Pole with the other guys but at that moment Leonard and Penny had no commitment to each other. She didn't want to interfere with his science projects and also wasn't ready to confess her feelings for him.
I Want You to Meet an Old Friend of Mine: There are several people on this show who also featured in Roseanne, first and foremost Johnny Galecki as Leonard. Sara Gilbert plays Leslie Winkle who briefly dates Leonard and Laurie Metcalf plays Sheldon's mom. Galecki also pointed out at a convention that his first kiss was with Mayim Bialik when he guest starred on Blossom years ago.
Leonard turned a non-date "hanging out" activity with Penny into an opportunity to confess to all the things that he let her get away with when they dated, generally acting very obnoxious and the evening turned into dirty laundry being aired out. Leonard later apologized for his behavior, only to learn except for the "dirty laundry" part Penny liked seeing him take charge and stand up for himself (showing signs of attraction to him). As they parted ways for the evening, he mused to himself "I am such an asthmatic dumbass."
Stuart occasionally complains that his comic book store isn't doing very well. But then why won't he sell Marvel comics? Look around and you'll see none in his store.
Stuart does sell Marvel comics. Either that, or Sheldon produces a issue involving Wolverine with bone claws mighty quickly for somebody who doesn't drive if he can possibly avoid it, didn't take Leonard's keys to go home with, and didn't bring his bus pants with him.
Not to mention hosting Stan Lee for a signing.
He also sells Archie.
Idiosyncratic Episode Naming: Episodes are titled as theorems, postulates, conjectures, et cetera. And it is usually descriptive ie "The Nerdvanna Annihilation" involves Leonard contemplating selling his nerdy collection. Sometimes it's about something major to the plot, other times it's a throwaway line.
The episode "The Recombination Hypothesis" has a big one, almost the entire episode is Leonard considering whether to ask Penny out and the consequences that would follow. Later at the end, Penny imagines herself at a Shotgun Wedding heavily pregnant and at Leonard's side. She promptly decides to stop at the drug store before meeting up at the real date.
Leonard imagines how he could have handled a situation with Penny differently in "The Nerdvanna Annihilation" and has him become the hero by opening the elevator shaft and taking her down himself.
Raj has a series of daydreams about how Bernadette could leave Howard and they get together. Each one starts off normal only to progressively become weirder, culminating in a Bollywood dance number.
Amy has one which has Sheldon admitting he didn't like Amy because she was a distraction and he thought about her so much it made doing work even harder. It leads to him kissing her.
Penny: Howard, you're going to throw away a great girl like Bernadette just because you're holding out for some ridiculous fantasy? Howard: Hey, just because you settled doesn't mean I have to. Leonard: Excuse me, I'm sitting here. Penny: Hey, I didn't settle for Leonard. I mean, obviously he isn't the kind of guy I usually go out with. You know, physically. Leonard: Again, I'm right here! Penny: My point is, I do not judge a book by its cover. I'm interested in the person underneath. Leonard: (To Sheldon) I am here, right? You see me.
Raj gives a silent one, when everyone went to bed and turned off the lights, forgetting Raj was still there.
Sheldon: Please. Even assuming you could answer any question the way I would, the algorithms used by matchmaking sites are complete hokum. Howard: And that's exactly the answer we gave to the question, "What is your attitude towards online dating?" Raj: Howard wanted to write mumbo jumbo, but I said no, our Sheldon would say hokum.
Incessant Music Madness: Sheldon plays the bongos at three in the morning, wakes Penny and Leonard up, and doesn't stop playing when they tell him to.
Innocent Innuendo: Sheldon will often say things without making the connection that what he said is inappropriate or just sounds strange. One time Sheldon was on the receiving end when Leonard told him about his date with Amy that went well, although he hurt himself while dancing the Hokey Pokey. "Turns out she really knows how to get a guy to relax and have a good time. Though truth be told my groin is a little worse for wear."
Insane Troll Logic: Sheldon hates being wrong and when he can't refute something with normal logic he resolves to this trope to get his way, such as claiming to be a new evolution of mankind that are far more intelligent but incapable of driving properly.
It appears that Sheldon and Amy's made-up game "Counterfactuals" runs on this trope. For example, a question asks "In a world where mankind is ruled by a giant intelligent beaver, what food is no longer consumed?" The correct answer is "cheese danish" rather than "cinnamon" which is made of tree bark. They explain this as because of the Dams built to worship and appease the Beaver overlord, which would have left low-lying countries like Denmark completely flooded and thus deprived the world of its namesake confectionary.
Sheldon is not a rocket scientist. He's a theoretical physicist! Also, Sheldon takes great pains to point out that his team t-shirt spells "The Wesley Crushers" (Those Who Crush Wesley) and not "The Wesley Crushers" (Multiple People Named Wesley Crusher). Dr. Sheldon Cooper would also have you know that he's not crazy; his mother had him tested. She later confirms this (...though she should have followed-up with that specialist in Houston). Sheldon also does not play "pranks"; he subjects people to his classic pranks.
He also prefers it when accurate terms are used. One of the more notable things he prefers is to refer to sexual intercourse as 'coitus', probably to separate it from sex as in 'male or female'. (Note: Coitus actually strictly refers to heterosexual intercourse in which a vagina is penetrated by a penis and nothing else so calling any other type of sex this is inaccurate).
Repeated reminders that Howard does not have a doctorate
Also Howard would like to point out that he does not live with his mother. She lives with him.
Despite being presented as "exceptionally brilliant", he seems almost depressingly clueless to anything that isn't science-related (especially the most basic of social situations) making him something of a Genius Ditz.
He's not even infallible in his own area of expertise, having been corrected by Leslie Winkle, Raj, and the kid genius from Korea who turned out to be just as much an Insufferable Genius as Sheldon was. And the one time he gave Stephen Hawking a paper with a simple arithmetic mistake in the first pages. Meaning the entire 20+ page paper proving Hawking wrong was wrong.
Surprisingly averted more recently, when Sheldon discovered a process to create a new element completely by accident because of an error he made in reading the units on a chart (centimeters instead of millimeters). Oh, he certainly started insufferable, but to his credit once he learned of his error he insisted the others stop praising him, even though his discovery was confirmed by independent experiments, and his friends tried to remind him that many major breakthroughs came by similar strokes of luck.
Interrupted Intimacy: Sheldon is quite happy to interrupt Leonard and whoever his partner is in the middle of the act — for example, with Joyce Kim. Sheldon decided to interrupt by knocking on the door. Leonard was thinking of ignoring him, but Sheldon knew he was being ignored. Sheldon then came in to remind Leonard of their Roommate Agreement. Due to its terms, Joyce decided to leave.
By definition, this happened with Raj and Penny with the cliffhanger scene from the end of Season 4, showing them in bed together naked. However, Raj reveals in the Season 5 opener that they didn't actually have sex; Raj climaxed prematurely. Penny uses this information on him later to get him to stick with a reasonable explanation for the incident.
On the show, Howard's mother never appears onscreen while Raj's parents do. The irony is that Howard's mother is only heard yelling from the next room while Raj's parents appear on his computer screen when he video conferences with them in India.
In the fourth season Penny realizes that her love life has tanked (due to both lingering feelings for Leonard and the fact that her standards of intelligent conversation jumped significantly) while Leonard, Howard and even Sheldon are doing better than her.
Invented Invalid: Leonard makes up a story about going to a symposium to keep from going to Penny's recital. Sheldon feels that story is insufficient and makes up a more elaborate one that involves going out of state to visit a cousin in rehab, even going as far as hiring an actor to play said cousin.
It Will Never Catch On: "I assure you, you'll be sorry you wasted your money on an iPod when Microsoft comes out with theirs."
Inverted as a joke; in a flashback, Sheldon wants to iron out the Roommate Agreement to allow for time to watch Firefly, since he expects it to be on for years.
Wil Wheaton (at least, his character, not the man himself) for intentionally increasing the wedge between Penny and Leonard, just to get back at Sheldon. Although, it could be he didn't do that, and only implied he did to tweak Sheldon.
Sheldon: YOU DID THIS, didn't you! Wil Wheaton: Do you really think I would break up a couple, just to win a bowling match? Sheldon: No... I suppose not. Wil Wheaton: Good. Keep thinking that. Sheldon: Wheeeeeatooooon!
Jimmy Speckerman, who bullied Leonard in junior high. He gets drunk and apologizes but the following morning he demonstrates he's a Jerk with a Heart of Jerk.
Jerkass Has a Point: Wheaton said this just to win a bowling match, but he was right in that leading Leonard on would be more cruel than breaking up with him. Given later seasons, it feels like Penny is still stringing him along, since she is a lot more unsure about her own feelings than he is.
Sheldon shows concern and attention for his friends in his own ways, can offer genuinely helpful advice on their problems if he's in the right mood, he's never actively malevolent to them beyond verbal jabs, and is hurt if they slight him in some way. On the other hand, his perspective on social interactions are skewed, so he doesn't understand when he does something offensive or inappropriate, he's constantly flaunting what he considers his superior intellect, and while he can offer helpful advice on a problem at times, he's just as liable to interrupt their explanation of said problem to note he doesn't care. The Heart Of Gold is there, but it's deep down under a lot of arrogance and an Ambiguous Disorder.
Howard. While this becomes a more apparent factor of his character as the series progresses , there have been indications even from earlier episodes. He clearly possesses an ostensibly sensitive nature, there are severe implications that his flirtatious nature was based on a desire for genuine companionship (lampshaded to an extent when he enters a relationship with Bernadette). He undeniably possesses some degree of compassion and genuinely cares for his friends, most of his undesirable characteristics are associated with his overly confident and sexually frustrated nature (which are almost completely non existent when he and Bernadette officially enter a relationship).
Amy is a more clear example than Sheldon, she genuinely doesn't seem to realize how rude she can be (especially to Penny), but when she thinks Penny's depressed she rushes to cheer her up.