A metaphorically descriptive word first derived, then corrupted for illustrative and reactionary purposes from the original 'Christian' in the following progression: Xian, the traditional contraption for Christian, then became (rightly or wrongly) Xtian, Which then became Xstain as some indeterminate 'stain'.
Reactionary to the misspelling of atheism as athiesm and illustrative in the sense that Christians seem metaphorically to adopt their faith as a stain of indeterminate composition as opposed to thinking it though rationally. Indeterminism is exemplified in the undefinition of the Christian god (is it incarnate or what? Is it omni-everything or what? Is god an 'evolutionist' or a 'creationist' or what?). The stain is indicative of the persistence of the myth of Christianity over the ages in the face of all contrary evidence and thorough debunking of it.
The Xstain chose to come to an absurd conclusion about the existence of its vacillating theistic? Deistic? god, citing that it was his scientifically/logically justifiable (though ironically unfalsifiable) right of opinion, even though we were both looking at the same facts. What a dummy that Xstain was! Went into complete disconnect mode!
What stupid idiots on Yahoo Answers use in place of the real abbreviation, Xtian. Usuers of Xstain actively assert their abbreviation is correct, despite the fact that no one except the user uses that particular abbreviation.
Diethyl Ether Dinner Candle™ says Christians are Xstains. Sounds like a cleaning product