Above the Influence: Jimmy subverts the trope when he takes advantage of a drunk Samara on the anniversary of her late sister's birthday in "The Performance."
Absolute Cleavage: When the gang is at a Coolest Club Ever in "The Renewal," this is why Jimmy suggests it will be easy to find their classmate Stacey Milano. He tries using his hands to demonstrate their size, but this doesn't go so well.
Holly: "Melanie won't apologize to Lex, [Claire] won't forgive Samara, I finish the mile five whole minutes after everyone else, I get blood on my shirt, and Rusty hasn't even shaved his beard yet! Today sucks."
Auto Erotica: Stacey and Andrew in "The Distance". Later, Rowan loses his virginity to Kristen in the back of her van.
The Bet: Milo bets Tom he can deflower the latter's cousin Carrie when she visits for an episode. Tom, who wouldn't ordinarily tolerate such an act, goes through with the bet because he knows his cousin - and he wins. And he gives Carrie the money.
Better as Friends: Rusty went out on one date each with Holly and Claire in middle school, and that was the end of that. At least for a little while.
Blackmail: A favored method of Jimmy's, used several times over the course of the series.
Big Applesauce: Samara's family is from the Big Apple, and she moves on to NYU after graduation.
The Bro Code: Mike supposedly violates this for dating Iris after her breakup with Rick, but it is Rick himself who really breaks the rules by sleeping with Mike's ex Cassie and taunting Mike with the video of it.
Brooding Boy, Gentle Girl: While Kent isn't unhappy to the point of constant brooding thanks to good friends like Tom, Holly nevertheless expands his horizons and generally makes him feel better about himself.
But Liquor Is Quicker: Stacey is mentioned as a frequent victim of this, and Jimmy uses this method to sleep with Samara on the anniversary of her late sister's birthday.
California University: Played realistically, with the gang separating to attend different universities across the state (or country) at series' end.
Call Back: In "The Pinch," John (with Adam and Stacey) says "Mind if we join you?" before joining Holly and her friends for lunch for the first time, echoing Kent's "Mind if I join you?" from "The Crush".
Character Filibuster: Samara is prone to doing this almost Once an Episode, much to the annoyance of everyone else, but other characters, particularly Claire and Kent, will engage in a sizable speech if someone pushes their buttons enough.
Club Stub: In "The Club," Kent's attempt at creating an on-campus nature club fails spectacularly when no one shows up but himself - and later, Claire, who's trying to hook him up with Holly for the Homecoming Dance. Ultimately, the club shuts down after one meeting, and Holly ends up going to the dance alone.
Country Matters: Beginning in "The Switch," when Rod first calls Claire this for her overreaction to Kent's kissing of Holly (despite having not met either of the girls yet), the word is tossed around more frequently than it should, mostly in reference to this incident.
Detroit: Jessie's family hails from Detroit, where her father worked at a car dealership.
Diamonds in the Buff: Holly takes a picture of herself in the tub wearing only Kent's birthday gift for her (a turquoise necklace) in "The Distance." This doesn't become important until much, much later.
Disproportionate Retribution: In "The Sin," when Kent pulls Holly in for their First Kiss, Claire immediately calls him a rapist and inadvertently (via Rowan) ends up getting him sent to the office. The misunderstanding is cleared up, but not before Rod finds out and the trope is taken even further.
Rick joins this camp when he sleeps with Cassie and sends the video of it to her ex-boyfriend Mike in response to Mike beginning to date Rick's ex Iris.
Distracted by the Sexy: Rusty and Claire both have moments of this in "The Distance," when they both spend the day with each other in their underwear to get back at Jimmy.
Evil Gloating: Jimmy brags about cheating on Claire right after she finally tells him she loves him in "The Charm."
False Rape Accusation: In "The Sin," Claire calls Kent a "rapist" when he kisses Holly by surprise. Rowan overheard, and shortly afterward, Claire and Kent are pulled out of their history class and sent to the office for disciplining. There they settle their antagonism, but not before Rod learns about it, and he decides that Claire should be severely punished for what could have happened.
Hormone-Addled Teenager: In "The Stickers," Kent, Holly, Claire and Rusty make a pact to stop talking about sex until one of them actually loses their virginity, in an attempt to subvert the trope. It goes about as well as you'd expect.
Kent: "Milo, I think you have a gambling problem."
Milo: "Five bucks says I don't."
I Uh You Too: When Jimmy tells Claire he loves her, her decision to not tell him the same until she feels it is one of many things that helps to drive them apart. When Holly tells Kent she loves him over the phone while he's in New Jersey, he chooses not to respond until he gets back to California.
Joisey: Kent's parents are originally from here, and that's where the rest of his family lives, including his godparents, Aunt Theresa and Uncle Calvin, who specifically reside in Pemberton, part of the Philadelphia metro area.
Just Friends: Josh and Holly; John and Stacey; Kent and Rosalyn.
Tom: "...I know this is our lives and not some TV writer's script, but does anyone else think the whole 'Person A cheating on Person B' storyline is starting to get ridiculous here?"
Let's Wait Awhile: Kent and Holly are this way while dating, and so are Claire and Jimmy, although as part of his growing antagonism towards Kent, Jimmy becomes less patient as time goes by, enough to invoke a Scarpia Ultimatum to get Claire to finally sleep with him.
The Loins Sleep Tonight: Initially happens to a depressed Scott, which indirectly leads to Sloane cheating on him with Jimmy. Two years later, the same thing happens to a drug-addicted Jimmy, once again leading to Sloane cheating, this time with Rick.
Long Distance Relationship: Tom and Oriel, who live an hour apart in La Crescenta and Long Beach, respectively. Later, Melanie and Kristen.
Los Angeles: Specifically, set in the Glendale area, at the eastern end of the San Fernando Valley.
Malicious Slander: Claire calls Kent a "rapist" in "The Sin" after he surprises Holly with their first kiss. Thanks to Rowan, this simple overreaction gets she and him both sent to the office, at which point they settle their antagonism, but not before Rod finds out and Claire goes home with a new enemy. Months later, Jimmy and Rod team up based on their mutual hatred of Claire.
My Girl Is a Slut: Jimmy coerces Sloane into sleeping with Skylar so the latter can finally lose his virginity and so Jimmy can have an alibi for murdering Cameron that night, by saying he was with her that night.
One Steve Limit: Averted. There are two people named some variation of Sam, but one (Samara) is a student and main character, while the other (Sam Greene) is an adult and only occasional supporting character. In addition, there are also two minor supporting characters named Nicole: the first, Nicole Sullivan, is a classmate of the main cast members, while the second, Nicole Rivers, is the older sister of another classmate, Sloane. The trope is played straight after Nicole Sullivan and then Sam Greene are killed by Jimmy.
The Other Rainforest: Dana is a wildlife student at Humboldt State University, among the redwoods in northern California, and her influence is what ultimately persuades Kent to go there for his college education.
Sibling Triangle: Scott ends up in a brief one between his girlfriend, Sloane, and her older sister, Nicole, after they engage in Three-Way Sex per Jimmy's suggestion. Besides the Squick factor both sisters admit to, it becomes worse when Jimmy's plan to sleep with a disgruntled Sloane afterward comes to fruition.
Thanksgiving Episode: Holly and Kent meet each others' families and Claire opens up to her own about her flawed relationship with Jimmy in "The Parents," set on this holiday.
Their First Time: Jimmy and Claire consummate their relationship in "The Twist," with bad results. Kent and Holly attempt to lose their virginity in "The Charm," but the consequences of Jimmy's revelations earlier prevent them from thinking clearly and they are unable to continue.
There Are No Therapists: Subverted. Vanessa's mother Sherry is a counselor at the high school, to everyone with a last name starting with P through T - meaning Kent, Holly, and Samara are all among her assigned students.
There Is No Kill Like Overkill: Invoked in "The Renewal," when Jimmy and Cameron are discussing solutions to the latter's frustration with ex-girlfriend Samara:
A Threesome is Hot: Subverted. We don't see it, but when Jimmy suggests this to Scott as a solution to his problem, it ends up ruining Scott's relationship with Sloane (although it does fix the original problem). Of course, this was the plan from the start, enabling Jimmy to sleep with Sloane in the aftermath. After they break up, Samara and others invoke the idea that we're supposed to feel sorry for him about this.
Wham Episode: "The Charm," the mid-season finale of Autumn, in which, after Claire finally tells Jimmy she loves him, he immediately rejects her and gloats about his affairs with three other girls, two of whom are at the dance that night with other dates. Shortly afterward, Jimmy begins his secret collaboration with Rod.
Your Cheating Heart: Jimmy cheats on Claire (three times) after becoming suspicious of her relationship with Kent. Through backstory, we learn that Holly's mother Pam cheated on her father Mark; Claire's father Walter cheated on her mother Lisa; and Kent's (still-together) parents are both notorious cheaters to this day.
Barely subverted with Rick when he and Iris break up before he has the chance to cheat on her with Mila. Played straight again some time later when Mike is seduced by Kristen while in a relationship with Iris. Later still, Rick sleeps with Sloane (and possibly puts a bun in her oven) when she turns to him to escape from Jimmy's corrupt ways. Yeah, this trope is awfully prevalent in the series.