https://en.m.wikipedia.org/wiki/Euphemism
> Frequently, over time, euphemisms themselves become taboo words, through the linguistic process of semantic change known as pejoration, which University of Oregon linguist Sharon Henderson Taylor dubbed the "euphemism cycle" in 1974,[17] also frequently referred to as the "euphemism treadmill"
> Mentally disabled people were originally defined with words such as "morons" or "imbeciles", which then became commonly used insults. The medical diagnosis was changed to "mentally retarded", which morphed into a pejorative against those with mental disabilities. To avoid the negative connotations of their diagnoses, students who need accommodations because of such conditions are often labeled as "special needs" instead, although the word "special" has begun to crop up as a schoolyard insult.[