Insulting anyone's intelligence, regardless of the reason, is problematic. It's not fair to intellectually disabled people that they are used as the butt of a "joke" or insult, regardless of whether or not the person the insult is directed at has an ID. Intelligence is an ableist concept, with its most commonly understood definition rooted in white supremacy and other forms of bigotry.

I say this as someone with a literally genius IQ (145+) who often needs reminders to eat, take my medication, or attend routine medical appointments on time.