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1.
1. Somebody who is obviously lying, posturing, idly boasting, who does not have the goods; one who is 'so full of shit' that it would take four flushes during the movement to clear the bowl.

Originally from game of poker, c.1880, one who bluffs that they have five cards in a flush when they only hold four.
Steve: Phil doesn't really have a summer house?
Bob: No, he's living with his parents. He's a lying, four-flushing sack of shit.
by hactar May 01, 2003
 
2.
a person who makes false or pretentious claims; bluffer
Jane thinks she has everything, but all she is is a four flusher.
by jeteye June 28, 2010
 
3.
Bragging, boasting, and empty promise.

From 19th c. poker players - someone who is claiming to have a five card flush, when actuality they only have four cards. NOT someone who is so full of shit that you need four flushes to send them down the toilet.
In the movie "The Great Waldo Pepper" Robert Redford's character was exposed as a "Four Flusher" for claiming to have fought a German WWI ace, when he actually had not.
by Godzilla1960 May 25, 2014