- Cliché Storm: Deliberately, and a common criticism of the film.
- Hilarious in Hindsight: Disney and Pixar's Show Within a Show, Buzz Lightyear of Star Command, did a very similar premise for one of their episodes way before this movie was made. The irony being that Planet 51 is a CGI movie made by another company.
- Ho Yay: Chuck and Lem are basically flirting through the whole movie. Some of their dialogue lampshades this.
Skiff: I think Lem's saying he wants the closet.
- Propaganda Piece: Humanity is portrayed as a monstrous group of aliens who want to enslave everything else. It's used as a scare tactic to the public much the same as actual sci-fi movies did back in the 1950s. Special mention that the scare tactics were being used before anyone even knew that life existed beyond their world.
- They Wasted a Perfectly Good Plot: They could have done so much more with the Humans Through Alien Eyes concept, thrown in some weird alien biology, a few alien customs, and it wouldn't spoil the 1950s gags excessively, but nope, its just cliches, Toilet Humor, and a weak copy cat Earth all the way through.
- Values Dissonance: Sorta subverted, since, despite the film was created and produced in Spain, the scriptwriter was Joe Stillman, who is American. It's possible that Stillman decided to write the script based on how Americans perceive animation, rather than aiming at how Spaniards perceive animation (at least at the time).
- Visual Effects of Awesome: This movie looks well done for a rather small budget.