Lying Liar That Lies
An expression applied to a character (or person) who lies (usually when a significant lie is involved). Used frequently by Supernatural recapper Demian in his recaps for Television Without Pity and within the forums, foremost when refering to Sam and Dean, and especially John Winchester.
Origin, per Demian: "LYING LIAR WHO LIES arose to mock those who excoriated Missouri for LYING to Dean while blatantly giving Dear El Deano a pass whenever he did the exact same damn thing to just about everyone the boys have ever met."
The creator of Supernatural is often called a "LYING LIAR WHO LIES".
The phrase has gained some currency in the fandom outside of TWOP.