Invisible Pink Unicorn

The Invisible Pink Unicorn (IPU) is the goddess of a parody religion used to satirize theistic beliefs, taking the form of a unicorn that is paradoxically both invisible and pink. She is a rhetorical illustration used by atheists and other religious skeptics as a contemporary version of Russell's teapot, sometimes mentioned in conjunction with the Flying Spaghetti Monster.
The IPU is used to argue that supernatural beliefs are arbitrary by, for example, replacing the word "God" in any theistic statement with "Invisible Pink Unicorn". The mutually exclusive attributes of pinkness and invisibility, coupled with the inability to disprove the IPU's existence, satirize properties that some theists attribute to a theistic deity.
History.
Russell's teapot is an analogy first coined by the philosopher Bertrand Russell (1872–1970) to illustrate that the philosophic burden of proof lies upon a person making scientifically unfalsifiable claims rather than shifting the burden of proof to others, specifically in the case of religion. Russell wrote that, if he claims that a teapot orbits the Sun somewhere in space between the Earth and Mars, it is nonsensical for him to expect others to believe him on the ground that they cannot prove him wrong. Russell's teapot is still referred to in discussions concerning the existence of God.
The IPU seems to have become notable primarily through online culture: in addition to alt.atheism, where IPU frequently came up in discussions, there are now a number of web sites dedicated to her. An early documented reference to the IPU was on July 7, 1990, on the Usenet discussion group alt.atheism. Other sources concerning IPU state that she was "revealed to us" on alt.atheism.
The concept was further developed by a group of college students from 1994 to 1995 on the ISCA Telnet-based BBS. The students created a manifesto that detailed a nonsensical (yet internally consistent) religion based on a multitude of invisible pink unicorns. It is from this document that the most famous quotation concerning IPUs originated:
Concepts.
It is common when discussing the Invisible Pink Unicorn to point out that because she is invisible, no one can prove that she does not exist (or indeed that she is not pink). This is a parody of similar theistic claims about God: that God, as creator of the universe, is not subject to its laws and thus not physically detecting him tells us nothing about his existence or lack thereof. The Invisible Pink Unicorn is an illustration which attempts to demonstrate the absurdity of citing attributes and a lack of evidence as proof of a deity's existence. Her two defining attributes, invisibility and color (pink), are inconsistent and contradictory; this is part of the satire. The paradox of something being invisible yet having visible characteristics (color) is reflected in some East Asian cultures, wherein an invisible red string is said to connect people who have a shared or linked destiny.
There are humorous mock debates amongst her "followers" concerning her other attributes, such as whether she is completely invisible or invisible to most, but visible only to those who have faith in her (bearing similarities to "The Emperor's New Clothes"). Some arguments are quite elaborate and tortuous, satirizing the disputatiousness and intricacy of the theological debates that occur in many religions.
The Invisible Pink Unicorn is also used to de-deify religious texts. The goal is to have the reader experience the text without heavily loaded concepts that many readers will associate with omnipotence, or will read with an unquestioned faith. It is argued that when someone re-reads the same text with all direct references to God replaced with the Invisible Pink Unicorn, the reader may see the text in a new and more critical way: 
Similar concepts.
In 1996, a unicorn that no one can see was adapted as a teaching device at Camp Quest, the first free-thought summer camp for children established in the United States, by Dr. L. Wilson. As reported years later in the July 21, 2006 "Cincinnati Enquirer", "Campers must try to prove that imaginary unicorns—as a metaphor for God—don't exist."
Richard Dawkins alluded to unicorns in this connection in his 2006 book "The God Delusion", writing that "Russell's teapot, of course, stands for an infinite number of things whose existence is conceivable and cannot be disproved. [...] A philosophical favorite is the invisible, intangible, inaudible unicorn."
In the essay "The Dragon in my Garage" from the book "The Demon-Haunted World: Science as a Candle In the Dark", Carl Sagan uses the example of an invisible dragon breathing heatless fire that someone claims lives in his garage. The supposed dragon cannot be seen, heard, or sensed in any way, nor does it leave footprints. There is no reason to believe this purported dragon exists.
In the "South Park" episode "The Poor Kid", a strict agnostic couple tell their foster children that God "might" exist, but then again, it's equally possible that there might be a "giant reptilian bird in charge of everything". At the end of the episode, the bird actually does appear and eats Kenny.
Religious commentary.
The Church of the Invisible Pink Unicorn often faces criticism from monotheistic religions for comparing their sacred beings with a fantastic invented character as well as trying to masquerade it as a religion while lacking the scripture, principles, ideologies, and broader social community necessary to be considered a legitimate religion. Many followers have responded to these critiques by improvising new literature, rituals, and customs, frequently written as farcical narrative that parodies not only scripture and rites itself but also the perceived importance or relevance of such scripture and customs. Invisible Pink Unicorn scripture and customs seek to evoke the mysticism of the unicorn and to simultaneously lampoon similar literature in other faiths per the IPU's main tenet.