An awful, unreasonable, pathological liar. Often a self-obsessed deluted personality.

n. (metaphorical, yet, often simultaneously literal) one who habitually and effortlessly utters falsehoods in a most blatant and profane manner, all the while maintaining a lackadaisical appearance of ingenuousness; despite, or perhaps, due to the fact that their entire corporeal membrane is filled to bursting with an inexhaustible supply of foul, though nitrogen-rich fecal mendacities waiting to be excreted into their victims' ears

A person that lies about everything