Most TV programs pride themselves on maintaining an accurate and chronological continuity of actions between episodes and seasons, stringing together tightly-woven plot arcs that can last for years and require watching the entire series from the start to understand all the elements at play in a single episode.
Aqua Teen Hunger Force is known for having little to no continuity of any kind between episodes, much less seasons. As such, main characters (such as Carl and the Aqua Teens) are regularly killed or permanently mutilated without any lasting consequences, returning unharmed in the next episode (sometimes even in the same episode). Even minor characters which are killed for humorous value in one way or another regularly re-appear later with no questions or commentary. Characters which hate each other one episode may have no particular feelings at all by the next one. This is particularly true for Master Shake, several episodes of which have him antagonizing Frylock, Meatwad, or Carl until they move out, kill him, or swear they're never going to speak to him again, with all inevitably being forgotten and reset to normal. Major locations and objects (such as Carl's house and car and the Aqua Teen house) are also often completely destroyed without any damage carrying over into the next episode.
What this boils down to is being able to watch any given episode and not have to know a single thing about what preceded it. Each exists as its own 12-minute movie, in essence. There are exceptions to this rule and a few minor plot arcs (such as the "Marcula episodes" when the Aqua Teens' landlord has them cocooned in the desert for several episodes and the stories revolve around other characters occupying their house). This is part of the surreal humor and general "who cares?" attitude the show is known for, and why so many fans love it. Viewers shouldn't be confused.