These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ensemble Darkhorse: Special mention has to go to Glen Coco. To put this in perspective, he appears on screen for about 4 seconds, the only part of him shown is the back of his head, he does not speak, and we only hear a single line about him:
Glen Coco? Four for you Glen Coco! You go Glen Coco!
According to the special features, the Mathletes were the favorite characters of the cast and crew.
Fountain of Memes: A highly quotable movie, a lot of the lines from it have taken on their own meaning and get quoted frequently.
Karen in particular.
Fridge Brilliance: Regina's line referring to Gretchen's nomination for Spring Fling Queen, saying that "She's not even pretty." In the original script, Gretchen was intended to be average at best, ugly at worst - mostly desirable because of her expensive clothes and lavish lifestyle. When the obviously pretty Lacey Chabert was cast for the role, this line was left in, and rather than just a statement, it becomes an insight into Regina's character. She truly believes that she is the queen bee because she deserves it, because she is superior to Karen and Gretchen. YMMV on which girl is most attractive, but fans can all agree that each of them is gorgeous, and only Regina's inflated ego could have resulted in such a surprise at Gretchen's nomination.
Genius Bonus: The whole "We should kill Caesar" speech may just be a history report, but when taken out-of-context it sounds like something an actual Roman senator would say about Julius Caesar.
Though it also counts as a "Funny Aneurysm" Moment depending on your view, the movie follows Cady as she falls in with the wrong crowd and goes from a mild-mannered nice girl into a party-happy temperamental bitch...
Lohan's constant arrests and trips to rehab afterwards have led to the widespread idea that Regina got the last laugh on Cady in the end.
Cady sees two girls making out at the Halloween party and looks very dismayed.
This shot◊ has become surprisingly prophetic. note Yes, that is Lohan in the garbage bin.
Neil Flynn, who at the time was best known for his then-current role as the Janitor from Scrubs, plays a father so clueless and passive as to come off as almost purposely apathetic - which also very closely describes Mike Heck, Flynn's current role in The Middle.
At the end, Regina channels her rage into sports. At the climax of Red Eye, Rachel McAdams's character goes to town on the villain with a hockey stick. Also the high school photo of Lisa playing hockey in Red Eye is a screenshot from this movie.
Lizzy Caplan as Janis Ian. Anybody who's seen her in anything else she's done (especially True Blood and Masters Of Sex) knows that she is drop-dead gorgeous in real life. In fact, she almost didn't get the part, as the casting director thought she was too pretty at first. As such the costume designers deliberately gave her an alternative/goth type look, rather than trying to dress her down. Caplan's beauty is probably a contributing factor to the theory that Janis is a former Queen Bee.
Averted with Gretchen, who was originally written as a much homelier character who was only popular because she was rich. This was changed when Lacey Chabert was cast in the role, and while the occasional line to this effect still shows up, it can easily be written off more as cattiness than her actually being viewed as unattractive.
LGBT Fanbase: Ridiculously popular among both gay men and women, and is something of a modern faux-camp classic.
Misaimed Fandom: Oddly, this movie seems to be most popular with the same kinds of people that it mercilessly makes fun of.
And with Periphery Demographic: This movie is popular with a lot of guys, particularly those who had a thing for Lohan back in the day and are nostalgic for her pre-trainwreck career or are fans of McAdams, Seyfried or Chabert curious about their early careers. Also heavily related to Testosterone Brigade listed below.
And even a few SNL aficionados by way of Fey. Still very much related to Testosterone Brigade in this case.
Cady: Calling somebody else fat won't make you any skinnier. Calling someone stupid doesn't make you any smarter. And ruining Regina George's life definitely didn't make me any happier. All you can do in life is try to solve the problem in front of you.
Another very wise line from Ms Norbery: "You have got to stop calling each other 'sluts' and 'whores'. It only makes it easier for guys tocall yousluts and whores."
Sequelitis: Apart from the element of Jo creating a group of Anti-Plastics and the climactic football game, the film is pretty much a remake of the first film, without the laughs. Also Jo's friends turning against her is extremely forced.
Tina Fey repeatedly turned down offers to make the sequel. Now that the sequel was done without her, she regrets turning down the offer.
Unintentionally Sympathetic: Mandi's step-brother is really callous towards her. It's not exactly undeserved but since she seems to like him, Taylor can come across as a bit of a jerk and arguably even as a contributing factor to Mandi's bitchiness.