A Date with Rosie Palms: Not only do Casey's parents take away his phone and internet as punishment but they also confiscate his porn. Casey's Father tells him "No more flogging the bishop".
Aliens in Cardiff: Lampshaded and justified. When one character claims that it would be absurd for aliens to secretly invade via a High School in a small town and brainwash the population, another Genre Savvy charcter points out that this would attract a lot less attention than attacking a big city, which the whole world will notice. See the page quote.
And Some Other Stuff: Zeke's drugs are made from a mixture of "caffeine pills and some other household shit."
Beautiful All Along: Miss Burke is an evil version of this trope. All it takes to make her look sexy is fixing her hair, dropping her glasses, and giving her a red tank top... but this occurs after she's been turned into an alien puppet.
Though being played by Famke Janssen certainly doesn't hurt either.
Billing Displacement: R&B star Usher is featured prominently on the poster despite appearing in only five minutes of the movie. None of the other cast members were all that famous (at the time), while Usher is, well, Usher.
Body Horror: The parasite dehydrates the old Mrs. Brummel to the point where her skin falls off of her body.
Also, Marybeth's transformation into her alien form.
Book Dumb, Brilliant, but Lazy: Zeke is clearly very smart and resourceful, yet he's repeating his senior year because, instead of focusing on school, he chooses to concentrate on pursuits such as manufacturing drugs and dealing various illegal merchandise to other students.
Brick Joke: During the credits, clips from the movie are used to accompany all of the lead actors except for Jon Stewart. He's shown teaching again, only with an eye patch and his hand bandaged.
The Cameo: By Ain't It Cool News' Harry Knowles, of all people.
Clark Kenting: The popular girl Delilah, in order to avoid being recognized by the aliens (who are targeting the most popular kids in school so that they can infect the most people), briefly disguises herself as a nerd by putting on Nerd Glasses. It works about as well as you would expect it to work — she gets infected anyway.
Closet Shuffle: While breaking into the teacher's lounge looking for a scoop, Casey and Delilah hide in a broom closet when they hear teachers approaching. Here, they find the dead body of Mrs. Brummel and witness the school nurse get held down and infected.
Dawson Casting: Surprisingly little of it for a '90s teen horror film. The oldest cast members to play teenagers were 22-year-olds Shawn Hatosy and Laura Harris. Elijah Wood, meanwhile, was 17 when he starred in this film, while Jordana Brewster was 18. Josh Hartnett was twenty,making him only about a year or two older than his character (Who is mentioned as repeating the year).
And Harris technically gets a free pass seeing as she was actually the alien anyway.
Drugs Are Bad: Inverted. The alien parasites are dried out and ultimately killed by the meth-like drug that Zeke makes and then sells in the parking lot. This drug is used in order to test who has been infected with the parasite.
Also subverted, as it turns out they weren't really drugs at all. Zeke was just using caffeine pills.
Dumb Muscle: Stan, much to his dismay. He feels that his heavy involvement as the captain of the football team is damaging his academic performance, and that his teachers are giving him preferential treatment just because he's a star athlete. This causes him to quit the team in order to focus on schoolwork.
Everybody Lives: Surprisingly there is a total of two casualties in the whole film, none of whom are the main characters.
Everybody Must Get Stoned: At one point in the movie, Zeke forces everybody to take his drugs so that they could find out who is being controlled by the aliens. Intoxication Ensues.
Evil Overlooker: Marybeth's face at the back of the poster certainly qualifies.
Evil Teacher: The teachers are the first people to get infected, and spread it from there.
Fake American: Canadian actress Laura Harris as the Southern girl Marybeth, complete with a ridiculously over-the-top Southern accent. In-universe, this also applies to Marybeth herself, making it a justified example.
Fake-Out Make-Out: Subverted. While breaking into the school's storeroom to steal ingredients for his drugs, Zeke cites the trope to reassure Marybeth should they be caught. However the two aren't patient, and start making out regardless.
Fingore: Mr. Furlong is bitten by the alien specimen that Casey finds. It takes a nice chuck out of his pointer finger. Later, after having been infected by the aliens, he has all four fingers of one hand cut off by a paper slicer.
Five-Man Band: Not the variety used on this site, but the one used in The Breakfast Club — the princess (Delilah), the criminal (Zeke), the brain (Casey), the athlete (Stan) and the basket case (Stokely). There's also the new girl (Marybeth). Who turns out to be the Big Bad.
If you're going by the "standard" Five-Man Band formula:
Glamour Failure: In addition to the obvious lack of emotion characteristic of Puppeteer Parasites, people infected with the alien parasite can be discerned by their need to drink lots of water, as the things quickly dehydrate their hosts. This is also why Zeke's drugs are so effective against them (the drugs absorb water and dehydrate people).
Goth: Stokely, although by the end, she's turned into a Perky Goth.
Groin Attack: Near the beginning of the film, Casey gets picked up by a group of bullies, has his legs spread apart, and gets his crotch slammed into a light pole.
Hannibal Lecture: Used multiple times by the pod people against the heroes, but the big one is delivered by Marybeth. When she confronts Casey in the locker room, she tries to convince him that, by joining the aliens, he will be happy, and will no longer have to suffer through humiliation at the hands of his peers. When Casey refuses to be swayed, Marybeth simply gives up, tells him that it's too late and that the aliens have already won, and comes after him.
Impaled Palm: Coach Willis stabs a pencil straight through Principal Drake's hand and it makes a gruesome crunch when he yanks it back out again. She is understandably horrified.
When Zeke is selling pens full of drugs to some students, he tells them that the stuff is "guaranteed to jack you up." Casey later repeats this line before he stabs and kills Alien!Marybeth with one of these pens.
While snooping in the teachers' lounge, Casey tells Delilah that she can be "pretty cool sometimes" (i.e. when she's not being the Alpha Bitch). Delilah asks if he's hitting on her. At the end of the film, Delilah repeats this line to Casey, whom she is now dating.
It Was Here, I Swear: Casey ends up in this situation when he brings the police to the school to recover Mrs. Brummel's body. When they open the closet, the body has disappeared and been replaced with a Recussitation Annie Doll.
Lens Flare Censor: In reverse. The darkness is used to cover up Marybeth's naughty bits. It doesn't work so well on the DVD, though.
Lovable Jock: Stan especially when compared to the more jerkish football players.
The Mole: Played straight when Delilah gets infected. Slightly subverted with Marybeth, who, unlike most Moles, isn't working for the bad guys — she's their leader.
New Transfer Student: Marybeth has just moved to town from Atlanta. Or so she says.
No Ontological Inertia: Justified. After Zeke examines one of the parasites, he notices that it doesn't have all the necessary organs to sustain itself independently, and concludes (correctly) that there must be an alien queen with a telepathic link to all of her "offspring." Killing her would kill all the parasites, returning everyone to their normal selves.
Not Now, Kiddo: Even though the alien-controlled teachers make up a cover story for what he saw that would still realistically scare a teenager, his parents decide he needs counseling, search his room for drugs, and decide to remove his phone, internet and even his Porn Stash (which they seem bizarrely completely okay with). Because that's parenting.
Red Herring Mole: Before the heroes find out who the real head alien is (it's Marybeth), they go through a number of false guesses, including the principal and the coach.
Screw the Rules, I Have Connections!: Stan's teachers curve his grades because he's the captain of the football team. Unlike most examples, he's fairly dismayed by this, enough so that he quits the team.
Single-Biome Planet: The head alien is from a planet covered entirely with water. This is the reason why people infected with the alien parasite need to drink lots of water — the thing needs a lot of it, and it dehydrates people rather quickly.
Sorry, I'm Gay: Stokely pretends to be a lesbian in order to prevent guys from hitting on her.
Stunt Casting: R&B star Usher in a small role as one of Stan's fellow football players.
Sucky School: There is a scene early on that takes place at a faculty meeting, where they are deciding how to divide the school's budget. Much to the teachers' chagrin, money that could be used for buying new textbooks or putting on a School Play other than Our Town is instead directed towards the football team, because, as Principal Drake explains, they live in a football town.
Somewhat unusually for a trope like that, she doesn't think the football team deserves all the attention and funding, but it's what the parents want. She says something like, "My frustrated hands are tied."
Teacher/Student Romance: The infected Miss Burke hides in the back of Zeke's car, then attempts to seduce him when he's speeding away from the infected football team. Zeke then slams the car into a school bus, sending her through the windshield and decapitating her. She gets better. The final scenes imply that they Hooked Up Afterwards, which is at least marginally less squicky because he's been held back and is, presumably, of age.
Wait. It's implied that a character has sex with a woman who was infected with an alien parasite, was decapitated, had her head sprout tentacles and slither around, and then put her head back on... and your issue is whether or not he is legally of age?
Tomato Surprise: Marybeth faked her negative result on the drug test by sealing her nostril and turning her pinky finger back into a tentacle temporarily to remove the butt cap of the pen so the drug will fall through it, but making everyone think she sniffed it.
Voluntary Shapeshifting: During the climax, Marybeth switches between human and alien forms at will.
Write What You Know: Casey references this trope when trying to explain to Stokely why he believes that Invasion of the Body Snatchers was Based on a True Story.
You Don't Want to Die a Virgin, Do You?: A mild example. Stan and Stokely kiss before Stan goes out to see if the people outside are still infected, with Stokely remarking that she didn't want to have never done that.