Genius Ditz: Motor Ed is an unparalleled mechanical and engineering genius, so much so that Drakken has to turn to him for help when creating a doomsday vehicle. He's also an extremely ditzy rocker archetype who cares more about his mullet and cruising on some hot wheels than anything else. His plans often involve using his genius skills for some almost moronically simple goal, like stealing a rocket that could easily destroy everything for miles simply to make a hotrod to cruise down the highway with.
Genre Savvy: Several...primarily Kim, Ron, Wade, and Shego.
Señor Senior Sr plays this totally straight, because he learned his supervillainy in books and it's an eccentric hobby for him.
Good Scars, Evil Scars: Drakken's long, twisted scar on the left side of his face is definitely evil. Yup. That's how you know he's a bad guy.
Goofy Print Underwear: Ron's boxers are either a solid color or have polka dots. It's Mr. Dr. Possible who suffers the most with his neon-heart print underwear. Drakken and Shego find a load of Dementor's stuff in the timeshare lair, including boxers with a skull motif.
Gosh Dang It to Heck!: Barkin mitigates his blasphemy by saying "Cheese and crackers!" The worst Drakken says is "Oh, snap."
Kim gets jealous over Ron at almost the drop of a hat: she also gets jealous when he becomes good friends with Felix in "Steal Wheels," and gets very angry over the time he and Bonnie spend together in "Homecoming Upset" - a lot more justified that time, however, as they were dating at that point and Bonnie was doing everything in her power to run it in. To her credit, she manages to direct almost all her anger at Bonnie and not Ron.
Hive Mind: The Bebes. The Tweebs seem to have this as well.
Hive Queen: A strange variation. The Bebes decide to make Bonnie their queen simply because she is the one person that Kim hates more than anyone else and are hoping that this will give them an advantage.
Idiot Ball: Ron's intelligence varies from episode to episode, and sometimes he's just flat out clutching this ball. Kim gets it a few times, too.
Ron: Hello, Information? I'd like the number for 911 immediately please!
I Don't Want to Ruin Our Friendship: This is Ron's reason for not getting together with Kim before they did (Kim's reason is partially this, but mainly about peer pressure). The first time this is made explicit is "Emotion Sickness", when Kim was under Moodulator influence. The second time, occurs in So The Drama and almost leads into...
I Want My Beloved to Be Happy: Ron decides against telling Kim how he really feels, leaving her to attend the prom with Eric whilst he doesn't go and instead sits in Bueno Nacho feeling sorry for himself... where he learns that Drakken is using Bueno Nacho as part of his new plan, leading to the reveal that Eric is a synthodrone, and allowing Ron the chance to confess to Kim, who returns his affection.
If I Had a Nickel: In "Ron Millionaire". "If I had a nickel for every time I heard that [talking about Bonnie's comment]...I could have grande-sized!"
He then literally gets a nickel for every Naco sold by Bueno Nacho, resulting in 99 Million dollars.
In the episode "Cap'n Drakken":
Shego: If I had a doubloon for every time I've done that (saving Drakken's booty)…
Irony as She Is Cast: Hidden Talent reveals Kim cannot sing high notes. In fact she is truly atrocious at it. Christy Carson Romano, her voice actress, is in fact an accomplished singer as she demonstrates at the end of the episode.
It Only Works Once: "Queen Bebe": Kim sees that the robotic villains, the "Bebes", no longer respond to radio interference like they did in "Attack of the Killer Bebes". This makes sense, as because the Bebes (and Kim) are moving at hyperspeed, a hypersonic emission would be much slower, and as such would not have the same effect.
It's Personal: "Car Alarm". Jim and Tim emphasize the upgrades to the Sloth are because Motor Ed outran them.
Done doubly in "Team Impossible". Kim has had it with the so-called heroes and is wiping the floor with them and them some. Ron is basically eating popcorn, then Wade shows up in the flesh, because they spiked his computers, and he is really mad.
Join or Die: Gemini tries to force Ron Stoppable to join his terrorist organization of WEE by threatening him with a laser.
Laser-Guided Karma: A good example happens to Bonnie. It is revealed that she was the only senior in Middleton High who wasn't graduating because she missed an important quiz on the last week of school, forcing her to attend summer school.
Laser Hallway: Kim's first mission involved the in-universe mother of these. More appear throughout the series.
Last Name Basis: Inverted with Shego. Her last name is "Go", but she has "She" in front because she used to be good and a part of a team with her brothers, and she was the girl of the team. It's also possible their names relate to their first names, but they're never given. Lampshaded by Ron in "Go Team Go".
LEGO Genetics: DNAmy's creations are an example, as are Drakken's customized clones.
Leitmotif: Kim, Rufus, Shego, Killigan and Monkey Fist all have their own themes, which made for an interesting climax in "Adventures in Rufus-Sitting", when the theme switches to whoever has the ball (well, molerat) at the time.
Lethal Chef: The school lunch lady fixes unrecognizable glop most of the time which may or may not be considered food. Kim also starts as this, and fan works tends to bring this to physics-defying levels, despite the fact she actually improved considerably at the end of the episode.
Limited Wardrobe: Many, many characters are guilty of this. (Bonnie wears her cheer costume an awful lot for someone supposed to be fashion-conscious.) Got better in Season 2 when the animators give both Kim and Ron got new rotating outfits. Ron was eventually returned to his jersey and cargos because the crew didn't like the "bowling shirt".
Bonnie lampshaded this on Season 1 (Episode 16) with the line "Kim Possible, you are such a loser! I mean you wear that same outfit, like, every day!"
Lock and Load Montage: The penultimate episode has Kim suiting up in battle armor, then picking up Ron in her Cool Car, like she is going to vape Drakken for keeps. Turns out it's for a puma in a tree.
Loony Fan: Cousin Joss Possible (for Kim, and at the end of the episode, Ron), later Frugal Lucre (for Drakken).