The term originates from the 1984 movie C.H.U.D. In the film, the acronym refers to a group of humanoid, flesh-eating monsters that were once humans, but mutated due to radioactive waste. While the word may have started pejorative use in 2003 to describe any repulsive person, its usage shifted as it became popular in the 2020s on sites such as Twitter and Reddit, after the podcast Chapo Trap House frequently used it to describe those who are ignorant or far-right. Source
I’m sorry, but it really wasn’t: