It means Canibalistic Humanoid Underground Dweller and originates from the 1984 film C.H.U.D. But is now used to describe ugly stupid people. Most notably in the Kevin Smith film Clerks 2(2006). The phrase is mostly used in America but is now starting to become popular in the UK.

the whale tail is the shape formed when a g-string rides up high over a womans trousers

An insult used primarily by people on the socialist left to describe conservatives, reactionaries (reactionary), members of the alt-right, libertarians, and even mainstream liberals. Generally the connotation of a very uninteresting and uncool male who contributes very little to society in terms of both productive work and original thoughts/opinions.
The type of person whose hobbies probably include watching "SHAPIRO OWNS SJW WITH FACTS AND LOGIC" compilations on YouTube, as well as jerking off to hentai (either traps or big anime tiddies).
They also tend to double as tape recorders.

This word has been in use in left wing circles in the northeast USA for several years, but it was popularized circa 2017-18 by the podcast Chapo Trap House.

Canibalistic Humanoid Underground Dweller

1.Acronym for "Cannibalistic Humanoid Underground Dweller"

2.The most dazzlingly significant piece of cinematic history.

Used to describe someone who is repulsively unattractive. Alternately, someone who is amateurish or unsuccessful in any given field.

Origin: Acronym for Cannibalistic Humanoid Underground Dweller. Originally from the 1984 horror film C.H.U.D. Further popularized by the 2006 Kevin Smith comedic film Clerks II in which the term was used as an intensifier to describe someone's unattractiveness (e.g. You ugly chud!).

A unattractive person whose defining characteristic of their personality is their egotism. Most often used to describe typically one-dimensional preps, chauches, or the like. A particularly mean insult; it should not be taken nor thrown around lightly.