MC Pee Pants first appears with a plan to get everyone addicted to candy as part of a "Global diet-pill Pyramid Scheme."
MC Pee Pants: A hyperactive juice that only I can produce
And fuel a giant drill, bore straight into Hell
Releasing ancient demons from their sleep forever spell
So they can walk upon the earth, and get re-situated
And Hock the diet pills that MC Pee Pants has created.
Why diet pills? What better for a population brain-washed into candy binges?
Meatwad and Carl are voiced by Dave Willis. Boxy Brown is also voiced by Dave Willis. Dave Willis is literally talking to himself in any scene with Boxy Brown.
Every seasons 1 and 2 episode opens with Dr. Weird, who seems a cilched supervillain, except he never does anything beyond experiment on his ill-fated henchmen. The protagonists for the rest of each episode are the Aqua Teens, who are introduced in the theme song as some kind of superheroes, but they're all deadbeats whose adventures are pure randomness caused specifically by their lack of heroics, intelligence and cohesion. Dr. Weird's prologues aren't random; they exist to help the Aqua Teen hilariously subvert the superhero genre. In most superhero shows the prologue would show the villain plotting his next scheme that the heroes would have to defeat; in this show, the villain is as much a deadbeat as the heroes, so they never meet as proper superheroes and supervillains should.
Why is Master Shake's flavor pistachio? Because he's nuts.
Although played for laughs, for Meatwad's young age, he is taken advantage of sexually quite often, even compared to Shake, who has entire episodes revolving around him being raped. Although this is meant to be a joke, Meatwad being molested by his guardian (and only ally) Frylock can be hard to watch in 'The Cubing'.
The hate and discrimination the Aqua teens receive may seem unjustified, but every now and again we are reminded just how nonhuman these characters are. With subtle cues that they're not biologically human such as their lack of sex organs and Master Shake enthusiastically eating humans in 'Circus', 'Dickesode', and 'Buddy Nugget', not to mention Meatwad's willingness to eat a man in 'Hands on a Hamburger'. Our earliest hint that they enjoy eating people actually comes from another one of Dr. Weird's creations, Willy Nelson, who unashamedly drinks the 'juice' from humans and ravishes their corpses. Likewise, psychopathy and manipulative behavior comes naturally to them the second they're inconvenienced, such as the entirety of 'Frylegs', 'Multiple Meat' and 'Super Birthday Snake', Shake talking a mentally ill homeless man into killing himself because he can't point out Jesus in a billboard in 'Gee Whiz', and Meatwad mentally manipulating Shake to get the house to himself in 'Super Model'. Humans have every reason to fear these beings as much as they do other Dr. Weird creations like Rabbot, Mc Peepants, and Paul.