These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Dude, Not Funny!: Authors Joel Eisner and David Krinsky criticized Diff'rent Strokes in the prologue of their book Television Comedy Series: A Guide to 153 TV Sitcoms in Syndication, claiming that the show was inappropriately labeled a comedy despite its adult-themed storylines. Examples cited included "The Bus" (from Season 3, where the boys are threatened by racists hoping to stop busing as a way to integrate their new school) and "The Ski Weekend" (from season 4, where Kimberly considers having sex for the first time with a boy she had met during an unchaperoned ski trip).
Too Soon: A brain hemorrhage, which could be termed as a FAM.
The episode "Little Mother", where Kimberly's childhood friend learns she's pregnant involves a misunderstanding where the boys mistake Kimberly herself for pregnant. Several seasons later, Dana Plato was fired when the writers refused to incorporate her own pregnancy into the show.
Values Dissonance: The whole premise of a couple inner-city black kids being "saved" by a kindly, paternalistic, rich old white guy may well provide this for some viewers.
Certain episode plots or events within the plot may be this for some viewers. "The Spanking" from Season 1 is a biggie, considering today's attitudes regarding corporal punishment. A lighter example occurs late in the show, when Maggie scolds Sam for wetting his bed. The family doctor later explains this was the wrong way to handle the situation, but it's still disconcerting, especially since Phillip reassures Maggie that she technically did nothing wrong. A plethora of similar examples exist.