As a proud member of the Untouchables I assume what you meant to say was "Just when I was beginning to think that NOT everyone from The Untouchables WERE completely retarded..." which would imply that you thought that almost everyone were retarded and then schmo confirmed that it was everyone.
What you DID write however was "Just when I was beginning to think that everyone from The Untouchables weren't completely retarded," meaning that you thought that every single one of us weren't retarded but then you saw schmo and realized that we did in fact have a retard among us.
Of course I wouldn't expect someone who generalizes a whole faction and assumes they are idiots to properly be able to use the English language to express what they want to say however, you need not worry because we, from The Untouchables have many people who are proficient in this field as we have graduated from high school and are able to act maturely rather than simply attempting to make unintelligible insults at other people.