Ear Worm: "Close your eyes, shut your mouth, dream a dream to get us out, dream dream dream dream dream dream..."
Fridge Brilliance: The Conspicuous CG is one of those tropes that breaks the illusion, and therefore the viewer has no suspension of disbelief... but that's the point; you're not supposed to think Planet Drool is real. The audience is just like the rest of the adults in the film that think Max's dreams are ultimately fake. It's not until Sharkboy, Lavagirl, and Mr. Electric come to Earth at the end that their existence is validated.
Lavagirl's representation in the real world (besides Max's mother) is a lava lamp.
When Sharkboy and Lavagirl first arrive in Max's classroom, Sharkboy pretty blatantly attacks Linus and rips up his paper. Now, that could just be his shark instincts acting up, but why would Linus have that effect on him? Well, considering the Big Bad for most of the film is Linus's counterpart...
The reason why the protagonists can't defeat Mister Electric with the Crystal Heart is because it can only be used by the Ice Princess, whose father won't let her out of the castle. At the climax, Mr Electricidad has to let Marissa go out to defeat Mister Electric.
Ham and Cheese: Those who don't like the movie will love Linus/Minus' overacting.
Tear Jerker: Max crying over Sharkboy and Lavagirl, who appear to be dead.
Toy Ship: In-universe examples: Max with Marissa and Lavagirl with Sharkboy.
The Woobie: Max. He's a bully magnet and just wants to be left alone to dream in peace. Interestingly inverted at the end when his own invention makes him realize that he's only been dreaming for himself and didn't care enough about others, implying that everyone else needed his help and The Woobie was actually all of them.
They Wasted a Perfectly Good Plot: So Sharkboy gets his own origin story, having been raised part of his life by sharks. What's Lavagirl's backstory? Never explained in the movie.