The process by which a pejorative term is replaced by a more
politically correct term, only to over time be corrupted and used pejoratively itself until a new term is introduced, upon which the cycle repeats itself.
So named because walking on a treadmill gives you the illusion of going somewhere, when actually not making any progress. Basically a form of
political correctness masturbation.
The best example of a euphemism treadmill is the word "retarded", which was
originally adopted as a more apt and kinder
alternative to previous medical terms such as "moron", "imbecile", and "idiot".
"Retarded" is currently considered a pejorative insult, so new terms have been invented such as "
special needs" and "intellectualy disabled" , which will in time become pejorative insults themselves. Thus retarded SJW's, downie parents, and the self-righteous will always have something to bitch about.