Something Ricked This Way Comes - S1-E9
Rick: Cute, your sister's boss gave me a microscope that would have made me retarded.
Morty: Ooh. Oh, boy, Rick, I, I don't think you're allowed to say that word, you know.
Rick: Morty, I'm not disparaging the differently abled. I'm stating the fact if I had used this microscope, it would have made me mentally retarded.
Morty: Okay, yeah, but I don't think it's about logic, Rick. I, I think the word has just become a symbolic issue for powerful groups that feel like they're doing the right thing.
Rick: Well, that's retarded.