Four Flusher is a pejorative term for a person who makes empty boasts or who continually lies.
The term four flushing traces its origins to the game of Poker during the 19th Century. Four flushing originally referred to a person who would misrepresent that they had a flush - a poker hand comprised of five cards all of one suit (hearts, spades, clubs or diamonds) - when they only had four cards of one suit.