"The Flaming Spittoon Acquisition" takes a jab at card battle games with the guys being initially disgusted with "Mystic Warlords of Ka'a'"s latest expansion adding Wild West characters to a fantasy-themed world, but find themselves unable to resist buying and playing it.
After a long episode of slagging off Star Trek V: The Final Frontier ("Dude, Star Trek V is the standard by which all badness is measured!"), the Vanity Plate included the following, after the main text: "Oh, and William Shatner, director of Star Trek V? Go ahead. Sue us." In the same episode, Sheldon insists The Motion Picture is worse than V, and the same vanity card includes a shot at George Lucas.
Sheldon: They can't just cancel a show like Alphas. They have to help the viewers let go. Firefly did a movie to wrap things up, Buffy the Vampire Slayer continued on as a comic book, Heroes gradually lowered the quality season by season, til we were grateful it ended.
Take Our Word for It: Sheldon running a red light while driving Penny to the hospital in "Rubber Duck Deficiency", as revealed in "The Excelsior Acquisition". The scene of him driving her ends with him stopping at a red light, without taking Penny's advice to even go the speed limit.
Although he later admits that he was lying when he said he hadn't looked.
Amy was constantly wanting more physical contact with Sheldon, even coercing him to snuggle . Later Sheldon and Leonard went to pick her up from a liquor store parking lot Leonard helped her to her feet and walked her to the car and she happily exclaimed "Looks like someone finally found 'Second Base!'"
That Came Out Wrong: In "The Roommate Transmogrification" when Raj proves himself to be a better roommate than Leonard, Sheldon compares Leonard to Homo Erectus saying that he, like Homo Erectus, has been replaced by something better. Raj then makes a comment he regrets.
Raj: I'm the new homo in town... that came out wrong.
Sheldon would often say Double Entendres and not recognize what he was saying as sounding weird or odd, with everyone explaining why. When the group offered to help Sheldon overcome his stage fright, they suggested that they name them after the X-Men. Sheldon appreciated the sentiment but suggested that since the X-Men were named after Charles Xavier, his team should be named after Sheldon Cooper and be called the C-Men.
Howard: Oh, no... that's not a good name.
Penny when she's doped up on painkillers and she asks Sheldon to help her get into bed.
Penny: *laughs* Sheldon has to get me into bed!
Bernadette has argument with Amy, talking about a feud between Howard and Sheldon over a parking spot. "I'm going home and I'm going to have SEX with my husband! Maybe we'll even do it in the parking spot! (blinks twice) That sounded dirty but I didn't mean it that way!"
That Makes Me Feel Angry: Sheldon is not good at reading people's emotions at all, so about the only way to tell they are upset or uncomfortable at all is for them to tell him outright.
Penny: Of course this makes me uncomfortable, can't you tell? Sheldon: I really have no idea, I don't really excel at reading facial expression and body lang... Penny: I'M UNCOMFORTABLE, SHELDON! Sheldon: ...thank you. That's very helpful.
Penny:I know you think you’re some sort of smooth-talking ladies’ man, but the truth is, you are just pathetic and creepy.
Howard: Um, so what are you saying?
Penny: I am saying it is not a compliment to call me doable. It’s not sexy to stare at my ass and say, “Ooh, it must be jelly ’cause jam don’t shake like that.” And most important, we are not dancing a tango, we’re not to’ing and fro’ing. Nothing is ever going to happen between us. Ever.
Howard: Wait a minute. This isn’t flirting, you’re serious.
Penny: Flirting? You think I’m flirting with you? I am not flirting with you, no woman is ever gonna flirt with you, you’re just gonna grow old and die alone.
Lampshaded by Stuart: "Blink twice if you are here against your will."
Also inverted as that was the only reason Amy Farrah Fowler was found as match to Sheldon.
There Is Only One Bed: Played with, Penny couldn't sleep in her hotel room due to Amy's night terrors and asked Leonard to stay with him and Sheldon, who was already asleep. 's bed (and his idiosyncratic method of sleeping, described as "Like getting into Dracula's coffin") and Penny knew she couldn't share his bed. So she and Leonard tried sharing a bed as platonic friends, with awkward enough results.
Sheldon: Look on the bright side. Leonard: What bright side? Sheldon: Only nine more months until Comic-Con. Leonard: [smiling] Oh yeah!
This Is Going To Be Huge: In the flashback episode at the end of Season 3. While making out the roommate agreement, Leonard asks if Friday night being Firefly night needs to be in the agreement. Sheldon responds that they might as well decide now, because the show is going to be on for years.
Those Two Guys: Howard and Raj, and their "ersatz homosexual marriage". Although they aren't as directly connected to Sheldon, Leonard and Penny (by virtue of not being neighbors or roommates), they do manage to do activities seperate from each other and the others but do play up the Ho Yay undertones in certain episodes.
Raj: "Don't worry, there was no funny business between us, not with two hundred pounds of Sailor Moon between us!"
Toilet Humour: Toilet Humour IN SPACE to be specific, in "The Classified Materials Turbulence", where the gang has to fix a malfunctioning zero-gravity toilet. To quote Sheldon: "Apparently there is no law of diminishing comedic returns with space poop".
Howard: All right, this is an exact duplicate of the Wolowitz zero-gravity human waste disposal system as deployed on the international space station. Raj: Don't you mean the Wolowitz zero-gravity human waste distribution system?
Sheldon had some flatulence problems after eating brussels sprouts in an episode where he becomes hyper health-conscious.
Sheldon: "Thursday night will no longer be cruciferous vegetables night."
Sheldon insists on having a specific time to use the bathroom and is proud to say that he is "as regular as a German train schedule."
Sheldon also kept a journal of his bowel movements since childhood.
Penny: That's disgusting! Leonard: No, what's disgusting is that he still keeps track.
There are many jokes referencing Leonard's lactose intolerance too, which makes him flatulent; although, this is never shown on-screen.
Sheldon: "Leonard, if you can eat this piece of cheese without farting you can sleep with my sister."
Toilet Seat Divorce: During Leonard's brief "official" relationship with Leslie, she broke up with him over the fact he had a preference towards String Theory (which Sheldon brought up) while she is on the Loop Quantum Gravity. To the average viewer this is ridiculous, but to these super-geniuses it is Serious Business.
Leslie: How can we have a relationship if we don't believe the same thing? How are we going to raise the children? Leonard: I guess we'll wait until they're old enough and let them decide what theory they would like for themselves. Leslie: You can't let them decide, Leonard; THEY'RE CHILDREN!
Took a Level in Badass: For a certain qualification of "badass." Leonard started off the series being painfully shy and uncertain of himself, it took him the entirety of the first season to officially ask Penny out. It's implied that interacting with Penny has helped boost his sense of self-worth and he progressed from being a nice, generic guy to becoming scathing Deadpan Snarkers and having more of a potential love life than just with Penny. Just with his interactions with Penny he is much more comfortable being assertive and teasing her than he was before, no longer feeling he has to be submissive to stay on her good side.
In parallel Character Development, we've also seen Penny Take A Level In Nerd. (The first  with a Double Takeat herself, while the studio audience applauds.) In addition to random science-fiction analogies, she has quite a bit more patience and higher standards when it comes to dating.
In ''The Werewolf Transformation", after missing a haircut, Sheldon "enters a world of chaos" and becomes about as badass as he could be.
Trademark Favorite Food: Whenever the eating together, it's Chinese food. Although it's not so much trademarked for Sheldon as it is ISO.
Sheldon: Did you get the chicken shredded? Leonard: Yup. Sheldon: Even though the menu says it's cubed, not shredded? Leonard: Yup. Sheldon: Did you get the low-sodium soy sauce? Leonard: Yup. Sheldon: Did you get the good spicy mustard? Leonard: Yup. Sheldon: Excellent. (beat) What took you so long?
But when it's just them, they seem to have (slightly) greater variety in their diet. They go to various restaurants, including the Cheesecake Factory where Penny is a waitress. Also, at work they have generic cafeteria food together in some cafeteria presumably on the Caltech campus.
It completely covers Sheldon though. He has a strict menu that he eats per day, for all days, and presumably snacks as well. The Chinese food has to be from Szechuan Palace. (Unfortunately for Sheldon, they closed years ago. Now his cashew chicken comes from Golden Dragon.) He's similarly disappointed to see that they've got Mumbai Palace, not their usual Tandoori Palace. When Penny makes french toast for breakfast, he complains that it's "oatmeal day". When Leonard and Penny leave, he comments that the food does smell good, then finishes with "too bad it's not french toast day" and dumps it into the trash. He also seems quite fond of milk and tends to drink it more often than expected, especially if the other diners have wine or champagne.
Inverted with Raj, who has expressed his distaste of Indian food many times.
And then there was the time Sheldon was alone and ordered Kadai Paneer. Consider: He can only order it when the others are away, because of Raj's distaste for Indian food, Howard's peanut allergy, and Leonard's lactose intolerance. His meals are usually very regimented, but in this instance he was willing to break the pattern to order it. No wonder he called it "a symbol of my independence."
Training Montage: Parodied when Sheldon and Raj intently study a whiteboard... complete with fast cuts and "Eye of the Tiger" playing in the background to a bunch of different camera angle cuts. Twice.
Trolling Translator: In one episode, Howard would "translate" for the selectively-mute-around-girls Raj via Raj whispering in his ear. At one point Penny and Bernadette ask the guys how Amy found out they went brides maid dress shopping without her. Howard immediately blames Raj. When Raj angrily whispers his protest to Howard, Howard takes the opportunity to put more words in Raj's mouth. It's this trope and not quite Translation With An Agenda because everyone knew Howard was being ridiculous.
True Love Is Boring/True Love is Exceptional: Ultimately runs the gauntlet of both tropes with Leonard and Penny. Penny's "type" at the beginning was the dimwitted, muscular, Jerk Jock kind of guy and gave Leonard a shot because he was so different and interesting. They enjoy being together but Penny was attracted to the other guys because they seemed a little dangerous and doesn't feel that kind of excitement with Leonard. Because he and the guys she used to date were both boring and exceptional in different ways her dating life crashed in season four.
Season six plays both ends, as Penny teased the idea of breaking up with him (again) because while she loved him it was a "different, boring kind of love," ultimately backing off only because of his Puppy-Dog Eyes. But when encouraged by the girls to visit him at work she was awestruck over seeing him in his comfort zone playing with lasers and holograms, finding the exceptional part of him again. A few episodes later in "The 43 Peculiarity" she said "you know I love you...", which was the first time she said it to him, and that manages to stabilize their relationship on both ends remarkably well.
Truth-Telling Session: On "The Irish Pub Formulation", Leonard's confession of having slept with Raj's sister Priya snowballs into one of these.
TV Genius: Parodied in , where Sheldon and Raj have a Hard Work Montage to Eye of the Tiger. It's literally just them staring at a whiteboard of equations.
Ugly Guy, Hot Wife: Downplayed, as Leonard is considered to be handsome and looks good together with Penny but he is ever aware that she is normally out of his league. The trope is deconstructed in the sixth season when he explains that it is hard to have guys far more attractive than him (at the least taller) hit on her when they are out together.
Uncle Pennybags: Sheldon, surprisingly. When Penny falls behind on her rent and her car breaks down, he freely gives her enough money to pay for both of them. Despite her assumption that Sheldon's obsessive tendencies would lead him to hound her, it turns out that he's incredibly lax when it comes to lending his money. He honestly doesn't care when it's paid back, as long as it eventually is.
Uncomfortable Elevator Moment: The elevator's been broken for the entire series, so instead, awkwardness occurs while climbing the stairs. Penny and Raj's sister Priya share (intentionally drawn out to make the audience uncomfortable) in Season 4.
Understatement: After he worked up the nerve to ask her out in the first season finale, Penny admitted to Sheldon that she knew Leonard had "a little crush" on her. Sheldon responded with "A little crush. I suppose so, like how Menelaus had "a little crush" on Helen of Troy."
Amy comparing Penny and Raj sleeping together with bestiality.
Unishment: Amy pretends to be sick far longer than she's actually ill because Sheldon takes it upon himself to treat her illness, including rubbing Vaporub on her chest and bathing her. When he finds out she's been lying, he regretfully informs he has to spank her. She can't believe her luck.
(After the first spank which causes Amy to just giggle excitedly) Sheldon: "Excuse me! You're not supposed to enjoy this!"
Amy: "... Then maybe you should spank me harder...?"
Sheldon: "...Maybe I will!"
Unlimited Wardrobe: Partially averted. While the characters have a very extensive wardrobe, they do repeat outfits from time to time, mostly the guys.
Unreveal Angle: Howard's mother is the comedic version of The Voice, but some episode tease the viewers by having her in situations where she could appear, like her son's wedding. She once appeared in "The Spoiler Alert Segmentation" in the background, but her face was hidden. It confirmed that she's obese.
The Unsmile: Sheldon provides the current page image in the episode "The Griffin Equivalency":
"We're here to see Koothrappali, not kill Batman!"
Unsympathetic Comedy Protagonist: Sheldon's self-centered egotism and condescending behavior ofhim the source of conflict for any given episode, even just by being sick and asking for help (his obnoxious neediness at that stage is dreaded by everyone). Howard's Casanova Wannabe and outright pervy behavior of the earlier seasons were also not meant to be endearing, although he gradually grew out of it. That said the show is based on every character being unfairly humiliated at some point, which has occasionally made them more sympathetic than intended.
Valley Girl: Penny falls into this from time to time, even though she's originally from Nebraska.
Vanity Plate: The Chuck Lorre Production notes which give you a split second to read a long paragraph. Even the short ones with a picture and a caption usually takes a Freeze-Frame Bonus to appreciate.
Verbal Tic: Penny likes to call people "Sweetie." In a bout of confusion Sheldon used it as evidence that she has feelings for him.
Penny: "I call everyone sweetie." Sheldon: "You tramp."
Vocal Dissonance: Bernadette normally has a fairly high pitched, squeaky voice. But there are times when she yells and sounds exactly like Howards mom. Which he finds to be hot.
Howard being the stereotypical television Jewish man will never be rid of his mother, in any form.
Vocal Evolution: Melissa Rauch's voice for Bernadette was always pitched higher than her own natural voice, but her first few episodes it was still fairly natural sounding. Later episodes it is quite higher, almost to Helium Speech. Funny enough, when Bernadette gets angry her voice lowers in pitch.
Carol Ann Susi as the voice of Mrs. Wolowitz has always had No Indoor Voice, but was slightly more muted and with less enunciation in her earlier "appearances."
The Voiceless: Rajesh, whenever he's with a woman — unless he's drunk.
Voice For The Voiceless: Howard, who usually just relays what Raj whispers into his ear (though sometimes Howard's annoyed comebacks imply what Raj said well enough). There are also times when Howard will lie about Raj said in order to deflect blame on to Raj. Since Raj can't talk to them, he has no way of refuting the comments.
Volleying Insults: Sheldon hates Leslie Winkle for being the only woman able to be actually more deliberately unpleasant and insulting to him than he could be to anybody else. Cue their constant rows when both meet.
His proposal is both cringeworthy and utterly hilarious. Subverted in that Bernadette sees it as the most romantic thing anyone has ever done for her.
Walk and Talk: The central hallway set is redecorated to represent characters consistently have to climb (usually Once an Episode). They use it for a Walk and Talk in addition to a couple of Uncomfortable Elevator Moments. The creators are actually quite proud of this, as it is a unique piece of set design that no other show can claim. Similar shows only get away with an "L" shaped hallway.
We Want Our Jerk Back: In a variation Sheldon balked at switching up his regimented dinner plans and refused to go to Raj's place with every. The rest of the group spent the Sheldon-free evening talking about how annoying he could be, only to realize the group felt empty without him around.
Howard: I think it's like Beetlejuice...we mentioned his name too many times!
Wet Sari Scene: Penny who is a waitress and hates her job, says she spilled a drink on herself at work. Leonard pities her, but she says it was the best day ever as she got her greatest tips.
Wham Line: From "The Grasshopper Experiment": "Where did my life go, Penny?" Context? Raj was drowning his sorrows and that was technically his first spoken words to Penny, establishing that being drunk counteracts his selective mutism.
When Raj behaved obnoxiously while drunk with Penny as his date to a People Magazine function, he tried to apologize while sober via handwrit. Penny refused to read the letter and demanded something verbal, after a few seconds of mustering up the courage he squeaked out "Sorry." which was the first words he has consciously spoken to her without alcohol.
After Leonard wondered what Penny's feelings were towards him, they had an argument over his neurotic, jealous behavior and she says "You're too hard on yourself, you know I love you so can you please relax because you are driving me crazy." Both are stunned almost to the point of tears.
When Sheldon permits a rumor that he and Amy are having sex (to distract from his subpar work) Penny asked him straight up if they will ever have sex. After a short monologue about his struggles in dealing with emotional and physical intimacy he concludes with "It's a possibility." Once he turns his back Penny silently starts freaking out, clawing Leonard's arm.
In the sixth season finale, Raj's female friend Lucy breaks up with him and he has a tearful conversation with Penny the next day. When Penny says that it's just the booze talking, Raj responds "No, it's not... I haven't had a drink since last night..." Pause as they both realize that he's been conversing with her TOTALLY SOBER.
Season 2 episode arc where Leonard dates a medical doctor, Stephanie, who sort of stealth-moves into his apartment. He spends that whole third episode trying to find a way to get her to move back out, but being diverted because she keeps jumping his bones. She isn't explicitly stated to have broken up with him (when he finally does spit it out, her response is to, well, jump his bones)... but by the next episode Leonard appears to be single again, with no mention of Stephanie.
This was also played with in an episode where Penny decides to stay in Leonard and Sheldon's apartment for the night. Raj walks out of the shot right before she walks into the room and asks to stay. Leonard, Penny, and Sheldon all have the whole argument about her staying there and then, once that's all over and it's decided that Penny stays, they turn out the lights and all go to bed. Cut to Raj, who was in the middle of eating a sandwich in the kitchen. He quietly leaves the room, looking like he has no idea what just happened.
In "The Psychic Vortex" Raj and Sheldon managed to acquire dates with intelligent and slightly geeky girls (one being played by Danica McKeller) named Abby and Martha, and even got a second date shortly after. What made these girls really unique was that the ice-breaker was Sheldon carrying Green Lantern's power battery at a party and they fully knew what it was; they ended up playing Rock Band back at Sheldon's apartment. Not to mention that Sheldon even appeared to enjoy talking with Martha (discussing Flatland among other things) with Raj and Abby making out on the chair. It can be assumed that Sheldon's asexual nature really disappointed Martha, and that took Abby away from Raj. But these were girls who could relate to them in interests, intelligence and were attracted to them because of it (not even Penny can really claim that with Leonard), so with no follow up episode it almost seems to be a waste.
What the Hell Is That Accent?: When Barry Kripke is first introduced with his strange speech impediment (reminiscent of Elmer Fudd), Raj asks "What part of America is that accent from?", but his question is summarily ignored. For the record, it's called rhotacism.
Who's on First?: D"The Alien Parasite Hypothesis" with Amy telling Sheldon about her reaction to Penny's ex, Zack. "Hoo."
Played with in The Bozeman Reaction, where Raj ends it quickly.
Sheldon: General Tso’s Chicken is no longer listed under specialties. It’s now under chicken.
Sheldon: Yes, General Tso.
Raj: Not Tso the chicken, so the question. So?
Will They or Won't They?: For the first season, Leonard and Penny. In the first episode of season 3, they do, although they break up at the end of the season. They get back together in season 5, for the 100th episode.
Wimp Fight: Leonard and Sheldon get into a fight at a seminar in the first season, which is largely a push, shove and slap fight. They are subsequently shown on YouTube and are clearly embarrassed over how silly they look:
Leonard: Oh geez. Does this suit really look that bad?
Sheldon: Forget your suit, look at my arms waving. I'm like a flamingo on Ritalin.
The wrestling match between Howard and Raj also counts, the fight being which of the two would be the superhero and which would be sidekick in their imaginary hero team. It consisted of over a half-hour of circling each other on the mat. Leonard fell asleep waiting for something resembling a fight to happen, though their "superhero banter" was above average.
Also the time Sheldon and Barry played one-on-one basketball for a vacant office. (They chose sports so that they would have a level playing field, since it's they're both equally bad at.) They go forty shots without sinking a single basket.
With Friends Like These...: It's not entirely clear on why Leonard, Howard and Raj are friends with Sheldon and vice-versa. They see him as a source of irritation and make fun of him behind his back. Sheldon meanwhile shows them no respect, ridicules Leonard and Howard's work, and is so stubborn, selfish and demanding that the gang agrees with whatever he wants to do because it's easier than arguing with him.
Penny once questioned how Jerkass Sheldon got any friends to begin with. The answer: "We liked Leonard." Sheldon managed to save Leonard's life and kept Leonard out of prison, so he's indebted to Sheldon, but Howard and Raj fall back to "We liked Leonard".
Although a scene in begin with cheerfully toasting having effectively driven Sheldon out of their lives, it ends with them all lamenting that they actually miss him. Apparently despite his personality faults and aggravation, they actually do like him... they're usually just distracted from doing so by how annoying he is.
Women Are Wiser: Played with. Usually Penny or another female character is the common sense of the group, but sometime Leonard or others, including Sheldon are the ones to point out things the others never seen.
Written-In Infirmity: Averted. When Kaley Cuoco (Penny) fractured her leg at the beginning of season 4, Penny was absent for a few episodes and no reference was made to her not being around. Once she returned the writers decided that her character would have a new bartending assignment at the Cheesecake Factory and be shot from the waist up behind the bar. A Vanity Plate was dedicated to new rules to ensure the safety of cast members, including any extreme activities (Kaley was injured while riding horses). This did result in Penny wearing fewer shorts and skirts, as Kaley got a fairly major scar from the whole thing.
Mayim Bialik injured her hand in a car accident before filming for season . Similarly to Kaley, no mention was made and they simply filmed around the injury by hiding it via camera angles and scenery obstructions.
Ye Olde Butcherede Englishe: An in-universe example. Sheldon complains that a renaissance fair gets away with any inaccuracies simply by writing "Ye Olde" in front of everything.
You Answered Your Own Question: When Penny tells Leonard that everything goes wrong with their relationship when they talk, she adds that she had a relationship with a guy named T.J. and they never talked.
Leonard: "Wait, if you guys never talked, what did you... Never mind. Stupid question."
Your Mom: Invoked by Raj in order to try to get Howard to let go of "The One Ring". Then Sheldon gleefully notes that if they turn on each other, he will get The Ring by default, Raj and Howard to decide to team up against him. Sheldon lists his mother's faults before they get a chance to, leaving them to bring out the big guns.
Raj: All right, not your mother. How about... your grandmother.